Water heater knocking.

[southfork21]

I have a 2011 312bhx Wildcat 5th wheel. I started to get a "knocking noise coming from the water heater. It only happens when I run the cold water while on pump (city water connection no noise). I contacted Girard water heaters tech support and was informed that the noise was coming from the water flow switch activating. It is activating when it senses a change in pressure on the cold water supply line. This should only be happening when the hot water is turned on, but in my case it does when the cold water runs. It just started this last season before this there was no noise. I am thinking it maybe a bad reverse flow valve near the water pump. I have checked for any water leaks and found none. I am wondering if anyone else has experienced this problem.

[VinceU]

Originally Posted by southfork21

I have a 2011 312bhx Wildcat 5th wheel. I started to get a "knocking noise coming from the water heater. It only happens when I run the cold water while on pump (city water connection no noise). I contacted Girard water heaters tech support and was informed that the noise was coming from the water flow switch activating. It is activating when it senses a change in pressure on the cold water supply line. This should only be happening when the hot water is turned on, but in my case it does when the cold water runs. It just started this last season before this there was no noise. I am thinking it maybe a bad reverse flow valve near the water pump. I have checked for any water leaks and found none. I am wondering if anyone else has experienced this problem.

Does gas begin to flow when the outlet is opened? Almost sounds like "water hammer" whch can be steam collapsing after local overheating by the burner. Just an idea. In my experience it happened when water got into HP steam piping, same effect.

[southfork21]

Vince thanks for the help.

No the gas does not flow and the water heater does not try to light. The noise will occur even if the water heater has not run for many hours.

[RSchleder]

I know that home water heaters do much the same thing when they get old and have an excessive sentiment buildup inside the tank. Perhaps you've been camping in a campground that has very hard water and your tank is limed up.