FYI about Girard:
The GSWH-1 (1st Gen) was put into Berks up to sometimes in 2013. It had a two position rocker switch inside. Early models had a water input sensor for which one of the switches position selected. Later Girard modified the unit (and even provided mod. kits) to make the switch select low or high burner rates.
The GSWH-1M (2nd Gen)can be recognized by having a temperature dial. The dial may miss-lead you that it has an incoming water sensor. Actually, you are the sensor and merely adjust to suit to get the water temperature that you want. Because you can vary the burner from 18,000 BTU/Hr to 36,000 BTU/hr in fine steps, it is why it is better then Gen 1. (I wish that I had it - LOL)
Remember that both units performance are affected by incoming water temp. and water flow rate, which is dependent upon your supply pressure.
Both units would work so much better if only the gas burner valve was variable and automatically adjusted by a smart controller which compares the output temperature to the users desired temperature.
The Precision Temp RV-550 works this way. I keep asking the forum if anyone has installed or used the RV-550. I am not a salesman for it, but it is what the Girard should want to be. Here is a link............
RV-550 – Tankless Water Heater for RVs and Trailers - PrecisionTemp