Isata 3 Freedom Edition Owners Only - Truma Combi Hot Water Poll

[Judge64]

Freedom Edition Owners - If you have the Truma Combi in Hot Water Mode on Boost Mix 2, how long does your hot water last when continuously running?

Please answer in the Poll above and comment if you like.



Our first few trips in the Freedom Edition have been either boondocking or electric only hooks ups so we had been conserving water. For the most part the Truma Combi Hot Water capabilities were adequate. Although last week on setting of HOT EL2, the wife ran out of hot water at the end of doing the dishes.

We currently have full hookups so the wife was looking forward to a regular shower last night. When we got to camp about 4PM I set the TC Hot Water to a setting of BOOST MIX 2 so that the burner and both electrodes were on. At 10PM the TC Display was not flashing so the water was at max temp. After about 3 - 4 minutes my wife ran out of hot water.

I was watching the diplay while she showered out of curiosity. About 2 minutes in it started flashing so it was going back to a heating mode.

I waited about 15 minutes before jumping into the shower. I decided to do a Navy shower. The water was luke warm at best and by the end of my Navy shower it was cold.


I have done a lot of reading on Forums.... especially forums in Europe where the Truma Combi is much more prevalent since van camping is more popular there. Consensus seems to be you just don't get much of a duration of hot water because the water chamber is so small at ~2.6 gallions.

I'm just surprised by the recovery time. My last two coaches had the Girard Tankless Water Heater that worked well for us. If you look at the Girard design the heat exchanger holds far less than 2 gallons of water. Granted, the burner flame is strong and right on the heat exchanger but we could have hot water for 10+ minutes without any issues if the water pressure was 45 - 55psi.

When you look at the design of the Truma Comb, the biggest difference appears the water chamber is not directly against the flame. There is a heat exchanger / air pocket between the burner and the water chamber. This heat exchanger must be where the two electrodes are located to provide forced air heat or hot water in EL1 or EL2 Mode. Then when the burner is active, the heat exchanger area gets heated from the burner and / or the two electrodes if in one of the two MIX Modes.

I'm just surprised that the water takes as long as it does to reheat; especially when the diesel burner is active. Diesel fuel has a higher energy density than propane by about 50% so even with the design difference vs the on-demand hot water heaters, I'd expect water to heat up quickly and recover quickly when using diesel.

From what I have read in the Truma documentation, the furnace demand will take precedence over hot water heating. What I don't completely understand is why? There aren't separate heating components for furnace vs hot water.... its all the same unit. Be that as it may..... its a moot point since it is summer and the furnace is not being used.


I just want to get a feel of other owners experiences as I ponder ways to improve / upgrade the hot water in the coach. I don't believe that I have any issues with my system; however, twice now the Truma Panel has said OFF for the Hot Water when I had it turned on and verified it was on. I know it was not a DC power issue because the clock on the Truma Display was still correct. I did a factory reset last night to see if that corrects anything.

They do make some very small 120V on-demand hot water heaters for sinks so I am considering whether I could fit one under the bathroom sink where the water filter is on the 24FW and tap into the hot water heater there to provide some additional hot water generation.

[bclemens]

When I took my initial trip, it was cold and the furnace was running and I had plenty of hot water. I think I always take a navy shower though when RV-ing, by habit.

I am used to the AquaGo, so when I turned on the Combi I hopped right in, not thinking. I promptly got back out, then realized the water heater bypass was still on. Once I did all of that, I think it was 10 minutes...I got in and the water was very hot. Some people do not like the Oxygenics, because it does not shut off totally, it has a small trickle, but I actually prefer that, if I need a little more water when soaping up.

The only other diesel system like this is from Aqua-Hot. We tested it, and it was very loud compared to the Combi.

[Judge64]

I installed a different model Oxygenics shower head that we had in our Super C. It has the same button and I don't have an issue with a little water dripping when it is off.


The hot water is not a big deal to me.... but the wife's a different story. She has a lot of hair and she didn't wash her hair last night and ran out. I know Beari was running into the same issue with his wife.

The performance vs the design is a little baffling to me..... but hey.... I'm not an HVAC engineer so I may be off base with my expectations for better recovery time.

I have to say the TC is a very quiet device all the way around.

I'm coming into the Service Center on the 19th so I can have the Sevice guys check it out too.

[xrpb11a]

Originally Posted by Judge64

I waited about 15 minutes before jumping into the shower. I decided to do a Navy shower. The water was luke warm at best and by the end of my Navy shower it was cold.

I never had a problem getting 4 minutes of hot water out of BOOST/Mix2 mode.
However, one time i put it in that mode via the CP control panel in the bedroom, but waited for about an hour or two before showering.
The shower water was luke warm, and I got an error code.
I looked it up and it was some kind of over temperature error.
I am assuming having the truma in BOOST mode and not using the hot water for some time triggers some kind of over temperature error.

Did you check the display before using the shower yourself to see if it was ready?

[xrpb11a]

Originally Posted by Judge64

When you look at the design of the Truma Comb, the biggest difference appears the water chamber is not directly against the flame. There is a heat exchanger / air pocket between the burner and the water chamber. This heat exchanger must be where the two electrodes are located to provide forced air heat or hot water in EL1 or EL2 Mode. Then when the burner is active, the heat exchanger area gets heated from the burner and / or the two electrodes if in one of the two MIX Modes.

I'm just surprised that the water takes as long as it does to reheat; especially when the diesel burner is active. Diesel fuel has a higher energy density than propane by about 50% so even with the design difference vs the on-demand hot water heaters, I'd expect water to heat up quickly and recover quickly when using diesel.

From what I have read in the Truma documentation, the furnace demand will take precedence over hot water heating. What I don't completely understand is why? There aren't separate heating components for furnace vs hot water.... its all the same unit. Be that as it may..... its a moot point since it is summer and the furnace is not being used.

From your explanation above, it sounds like when the furnace is ON, air is forced through the pocket/gap and out to the coach. The air probably takes most of the generated heat along with it, leaving little heat for the water tank.
That would also explain why the furnace takes precedence over the hot water, by design.

[Judge64]

Originally Posted by xrpb11a

Did you check the display before using the shower yourself to see if it was ready?

Yes... the hot water was ready. The Hot Water Icon was solid and not flashing. After my wife ran the water for 2 minutes it started flashing indicating it was heating again.


Ground water temps also factor into the equation a lot. In Florida this time of year the ground water temp is 80 - 90F. We are up in PA and I will bet the ground water temp is 60F.

This is the first time we have not ran the hot water off the fresh water tank so that could very well br a factor. The water temp in the fresh water tank is likely 70 - 75F, which would reduce the recovery time.

As an experiment tonight, I may change over to the fresh water tank to see if it performs better.

[Judge64]

Originally Posted by xrpb11a

From your explanation above, it sounds like when the furnace is ON, air is forced through the pocket/gap and out to the coach. The air probably takes most of the generated heat along with it, leaving little heat for the water tank.
That would also explain why the furnace takes precedence over the hot water, by design.

Ahhh.... you are right, sir! I wasn't thinking about the heat loss from the fan kicking on to generate forced air heat.

It was the German wording that got me. They made it sound like there was a mechanical system change that made heating air the priority...... when it fact it is the heat loss in the heat exchanger from blowing the hot air out of the chamber to heat the coach.

[xrpb11a]

Originally Posted by Judge64

Yes... the hot water was ready. The Hot Water Icon was solid and not flashing. After my wife ran the water for 2 minutes it started flashing indicating it was heating again.

To clarify, did you check the hot water icon again before you got into the shower after your wife?

[Judge64]

Originally Posted by xrpb11a

To clarify, did you check the hot water icon again before you got into the shower after your wife?

I checked the hot water icon before my wife started her shower to make sure it was at temp.

After 2 minutes into her shower it started flashing.

It was still flashing when I jumped in so I knew I would likely not have much hot water.... and I didn't as expected.

[xrpb11a]

I plan to test the hot water time again this weekend, in sacramento, where it's gonna be in the 100's. It'll be interesting to measure the water tank temperature and see how much the hot water availability time changes from when I last measured it in March/April.
I always use BOOST/Mix2 mode when showering, so I'll also measure the recovery time after running out of hot water, and insure the Truma stays in BOOST mode.

Originally Posted by Judge64

I checked the hot water icon before my wife started her shower to make sure it was at temp.

After 2 minutes into her shower it started flashing.

It was still flashing when I jumped in so I knew I would likely not have much hot water.... and I didn't as expected.

[Judge64]

Originally Posted by xrpb11a

I plan to test the hot water time again this weekend, in sacramento, where it's gonna be in the 100's. It'll be interesting to measure the water tank temperature and see how much the hot water availability time changes from when I last measured it in March/April.
I always use BOOST/Mix2 mode when showering, so I'll also measure the recovery time after running out of hot water, and insure the Truma stays in BOOST mode.

Excellent!

Please report your findings and I will as well when I see if running off the warmer fresh water tank makes an appreciable difference.

[Judge64]

This may be an option to supplement the hot water.

It is 9.63" W x 6.25" H x 2.75" D so it could fit under the bathroom sink, behind the toiler or in the space behind the Power Control Center.

I would try to plumb into the hot water line coming out of the Truma Combi so it would not need to kick on at all until the water cools off coming out of the Truma.


https://www.grainger.com/product/6DX...E&gclsrc=aw.ds

[bclemens]

Originally Posted by Judge64

Yes... the hot water was ready. The Hot Water Icon was solid and not flashing. After my wife ran the water for 2 minutes it started flashing indicating it was heating again.


Ground water temps also factor into the equation a lot. In Florida this time of year the ground water temp is 80 - 90F. We are up in PA and I will bet the ground water temp is 60F.

This is the first time we have not ran the hot water off the fresh water tank so that could very well br a factor. The water temp in the fresh water tank is likely 70 - 75F, which would reduce the recovery time.

As an experiment tonight, I may change over to the fresh water tank to see if it performs better.

Ah yes, this would be a major factor on recovery. I was boondocking, so running off the tank.

[Judge64]

Originally Posted by bclemens

Ah yes, this would be a major factor on recovery. I was boondocking, so running off the tank.

Yep......

I'm going to switch over to the fresh water tank tonight and then compare the difference to last night.

I'll report back with the results.

[Judge64]

Did some more real-world testing tonight.....but I broke the cardinal rule of experimentation.... I changed two things at the same time.

I read in one of the forums over in the UK about a guy having issues with setting the hot water at night and then the next day it was cold or lukewarm at best. Sometimes it was hot in the morning but other times it wasn't. He spoke with Truma and tried a few things but it didn't help.

He then went into the Truma Control Panel and into the Configuration page and did a system RESET. After he did that it seemed to fix his issues..... at least short term..... but he never really reported back again.

I did the RESET this morning as well. That was change number one.

Tonight I switched over from city water to the fresh water tank. That was change number two.

After the remnants of Debbie blew by here in western PA, things cooled off a bit. We had the windows open all day and the coach temp got up to 78F. I used a digital thermometer to measure the water temp from the bathroom faucet tonight and it was about 71F. A little cooler than I thought it would be given I have a lot of electronics now in the fresh tank compartment and with the battery compartment also venting under the bed.

Before taking my shower I looked at the Truma Control Panel and it was flashing in the HOT EL2 Mode so I knew it was heating. I then set it to BOOST MIX 2 and waited for the icon to stop flashing.

I decided to shower first and take a regular shower for a true test. The water was pretty dang hot and I had to mix a fair amount of cold with it. I didn't take a long shower but I never turned off the water and after about 3 - 4 minutes I still had very hot water. When I got out it was flashing again so I knew it was in recovery mode.

The wife will probably take a shower later so we will see how she does. The fact that she ran out of hot water pretty quickly last night and I only had lukewarm water makes me think that maybe the Reset did something but I can't rule out the ground water vs fresh water temp differential either. I will turn the city water back on in the morning and test its temperature as well to get an accurate temperature differential between the two.

The other thing I am keeping my eye on is I put the unit into BOOST mode a couple times yesterday and last weekend and then when I went back and looked a while later it was in HOT mode. I am fairly certain that it should stay in whatever mode you select. I'll see if the RESET I did does anything to solve that issue.

[Judge64]

The wife took her shower and it was the same length as last night and this time the hot water lasted and it was hotter than last night.


And I may have uncovered the issue..... or at least a related issue.

Back in May I worked with FireFly to confirm a bug in their software controlling the Truma Combi and also reporting the proper status. I explained the issues I was having with the FireFly and they setup the system in their lab and confirmed there was an issue with the FireFly properly controlling the Truma and reporting back accurate status.

Since I did the RESET on the Truma Control Panel, the FireFly Display has stopped reporting any status information for the Trunm Combi and it only says.... Truma Display Busy

When I would access the Truma Combi from its own Display, I would see the Truma Display Busy message for a minute or two on the FireFly Display after I was done adjusting the Truma parameters from its own display. Then that message would disappear and the Truma status would reappear in the FireFly Display.

Now since the RESET the FireFly is not reporting any Truma Combi status and it just says Truma Display Busy.


So doing a RESET on the Truma Display has impacted what is happening on the FireFly Display. I am scheduled for Warranty Service at Dynamax on August 26th so I am going to add this to the punch list in case the FireFly - Truma bug has more to it than what I originally discovered.

Perhaps the bug in the FireFly software was screwing up the control of the hot water snd resetting the Truma corrected the issue?

Also.... the delta in the ground water temperature to the fresh tank temperature was ~10F. The city water temp was reading ~61F. So that is certainly significant.

So perhaps the RESET and the switch to the fresh water tank both helped to improve the hot water tonight???

[Judge64]

When I got up this morning, the TC was still on Boost EL2 and the water was hot, which is where I set it before going to bed. I don't leave the diesel on while sleeping so it is not using it when no one will be using the hot water.

The FireFly is still saying Truma Display Busy. The FireFly app is saying the same thing as well.

Once I found the FireFly bug back in May, I stopped using the FireFly and app and only have used the TC Control Panel.

Doing the RESET has done something. Perhaps it has resolved the conflict with the FireFly Display and the Truma Control Panel is the only thing controlling the hot water?

One of the bugs in the FireFly is that it would give a message that the 120V electric for the Truma is not available even if you are on shore power or you are using the Inverter when trying to use EL1 or EL2. I wonder if when trying to use any of the electric settings, the FireFly was overriding it because it thinks electric is not available?

It is very possible the FireFly and Truma Control Panel were fighting for control. When I was setting the mode on the Truma Control the bug in the FireFly might be overriding it?

Anyway.... I'm adding this to my Punch List so Dynamax can investigate it further with FireFly and Truma when I head to Elkhart for service.

[Judge64]

Another test with better results this morning after doing the RESET yesterday.......

Last week when I had the hot water set to HOT EL2, my wife ran out of water after filling the tub in the kitchen sink to do dishes using the fresh water tank.

This morning with the hot water set to BOOST EL2, my wife has plenty of hot water filling the tub and there was still hot water available..... and I am back on City Water this morning where the water temp is 10F colder.

The only difference in temp between HOT and BOOST is 4F so I am even more convinced the RESET fixed something. Last week were were running on the warmer fresh tank and this morning we are on colder city water.

The big difference with BOOST appears to be that it overrides the furnace for two heating cycles and keeps the water hot for 40 minutes. Since I'm not using the furnace, then BOOST should just be working pretty close to HOT.

I'm also pretty sure last week that it switched from BOOST to HOT on its own so that may have also been a factor as well.


After doing a little more digging into the message on the FireFly Display I see that the status LED is solid grey and it has two meanings..... either the Truma is being adjusted at the Truma Control Panel or the Truma Module is not connected to the FireFly network.

So doing the RESET may have temporarily disabled the communication between the two systems so the Truma Control Panel is completely in control.... or it broke the Firefly module for the Truma because if I try to do anything on the FireFly nothing happens. When I get back home later today I may cut the 12V to reboot everything to see what happens and if it goes back to the way it was working before the RESET.

[Judge64]

Argggghhhhhh..... I got my hopes up too soon.


Since I have full hookups I decided to take advantage of it to do some more testing. I set the hot water to BOOST MIX 2.... the max hot water generation.

The Truma Control Panel showed a solid icon for the hot water, meaning it should be at 144F. I set a timer and opened the kitchen faucet on full hot. The hot water only lasted 2 minutes 30 seconds. The hot water icon started flashing around 1 minute 30 seconds.

So.... I thought maybe that wasn't a fair test. You won't take a shower with it in full hot. So I let the TC heat back up until the icon was solid again. I had my timer set and it took 31 minutes to heat up the ~60F city water to 144F.

I do know the unit should have the diesel burner firing because I could feel warm air coming out the exhaust vent outside. I also know the two electrodes were on because they were drawing 14A.

And while I was waiting for the hot water to reach full hot, I happened to the FireFly was back online and reporting its status. It was offline for 12 hours and I did not cycle the 12V so it just came back on its own.

I then reset the timer and opened the kitchen faucet and adjusted the temp to a shower comfort temperature of about 106F - 107F.

This time the hot water icon didn't start flashing until 3 minutes. A that point I had to start reducing the amount of cold water mixing to maintain the temperature around 106F.

Then about 4 minutes and 30 seconds I was completely out of hot water with an incoming water temperature of ~60F.

I will try to rerun this test again using just the fresh water tank to see what an increase of 10F for the incoming water temp does for extending the hot water.

But I am going to seriously consider supplementing the hot water. A 30+ minute cycle time to get 4 - 5 minutes of hot water is just not ideal for us. I suspect 70F water will only gain about a half minute.

[Judge64]

Doing more research on the Combi........ and the performance specs are a bit confusing vs the actual settings..... and sorry for the long posts but there is a lot of stuff here I'm trying to sort out.


One the surface, it would appear that a hot water setting of BOOST MIX 2 would give you the highest energy generation to heat the water. MIX 2 means that the diesel burner and both electrodes are heating.

However, when you look at the specs on the website it says the following:

Energy input rate (gas / diesel mode)
Level 1: 7,500 BTU/h (2.2 kW)
Level 2: 14,300 BTU/h (4.2 kW)
Level 3: 20,400 BTU/h (6 kW)


Energy input rate (electric mode)
Level 1: 850 W (2,900 BTU/h)
Level 2: 1,700 W (5,800 BTU/h)


Energy input rate (mixed mode)
14,300 BTU/h (4.2 kW) + 1,700 W


Now they only list one "Mixed Mode" but based on the specs you have to think this is MIX 2 because it appears when both electrodes are used, they generate 1,700W / 5,800BTU of power.

The interesting thing here is they only list 14,300 BTU from diesel for the mixed mode. According to the specs, this implies more energy is generated in the diesel only mode because Level 3 lists 20,400 BTU. I'm assuming Level 3 means BOOST since the other two settings are ECO (Level 1) and HOT (Level 2).

The other thing is they only list one mixed mode in the specs when there are two on the Truma Control Panel. You have to assume the specs are providing the energy for MIX 2 because the 1,700W mean both electrode have to be on to generate that much power.


The other interesting things is they have a spec for heating hot water. They say on HOT Mode it should only take 23 minutes for 59F water to reach 140F.

When I was set to BOOST MIX 2 yesterday, it took 31 minutes for it to reach 144F with 60F water. Hard to believe it took 8 additional minute to bring the temp up 4 degrees from the 140F HOT spec to the 144F BOOST spec.


Now since Truma only lists one mixed mode in the specs, you would think they would list the max energy generation. Why would they list the maximum for both electrodes but only the middle energy for the diesel?


Perhaps there is some limitation in the mixed modes because of engineering limitations of the unit itseld? Perhaps the Combi is only designed for a maximum output of 20,400 BTU?

Since they only list 14,300 BTU/h + 5,800 BTU/h for their mixed mode spec, that might seem to be the case since this is only 20,100 BTU.

This would explain why they don't list a spec of 20,400 BTU + 5,800 BTU for a MIX 2 mode for a total of 26,200 BTU.


This might be why it took 31 minutes for the system to get to 144F at 60F water temp instead of something closer to 23 - 25 minutes. Mixing diesel with the electrodes may not be as efficient as just using diesel to heat the water on its own.


So its back in the lab to do some more testing. After looking at the specs in detail on the website and in the manual, I am starting to believe that using BOOST and diesel only might be the most efficient and fastest way to heat water........... and mixing diesel with the electrodes doesn't necessarily mean more power generation. It just means balancing diesel with electric to generate the same amount of power without burning more diesel to do it.