Do you have a thermal expansion tank on your water heater?

[5030]

All good points.

My hydronic floor heat uses tankless heaters as well as our domestic water supply heater. System water pressure against it all the time. Check valve to protect the system from water that's in the floor system. Expansion tank to protect the floor heat system from cyclic pressure changes.

Only place I have one is on my in floor PEX heat system in the shop and only to mitigate cycling pressure spikes when transitioning from idle to heating modes, but the entire system if full of Cryotek so no tap water ever see the system.

 

[laurencen]

have on on the shop infloor heating also it runs usually at 12.5 to 14 psi, if the tank was not in place likely double those pressures from cold to hot

 

[Katahdin]

I have a 23-year-old system with a well, Burnham/Beckett oil fired boiler, and a detached hot water tank. Both the boiler and hot water tank have expansion tanks and when they go bad the safety relief valves release water during a heating cycle. So, I definitely see pressure problems without them and I'm now on my 3rd set of expansion tanks.