Hot Water Heater issue

Michael_27

I recently turned the gas hot water boiler in my house on and several days later I noticed my gas hot water heater was spitting hot water from the relief valve at the top. The hot water heater itself is working fine and when I shut down my boiler the situation does not appear to be happening. Could this mean the thermostat on the boiler is not working? Any information or guidance would be great.

Brad White_9

Couple of Thoughts

Is your boiler pre-heating your domestic cold water on the way to the hot water heater? And might there also be a charging pump between an immersed boiler coil and the DHW heater?

The water heater valve is a T&P (Temperature and Pressure) valve which will open at either 150 PSIG or 210 degrees F.

My thinking is that the boiler being on might be overheating the water regardless of what the water heater itself wants. This means tripping on temperature.

Another thought is, if there are any check or non-return valves and no domestic side expansion tank for the captive volume, it may be tripping on pressure.

Michael_27

Hot water heater issue

Thanks for the input. I think your first guess that the boiler is pre-heating the domestic hot water and causing excessive pressure in the DHW tank is correct. What typically would cause this situation, a faulty temperature control on the boiler? Any suggestions again would be great.

Brad White_9

Either

a faulty boiler operating high limit (may be set to say, 180 but is bouncing off of it's safety high limit which could be 220 or more God Forbid.

Before doing anything silly (or me suggesting same) can you monitor the pressures and temperatures in the system components? A surface pipe temperature if not the boiler dial thermometer is good. On the DHW side a hose-bibb pressure gauge attached to a drain valve is handy. Watts makes them and they only cost $7-8.00.

At least then we can go for symptoms instead of hypotheses. Can you get those checked?

Brad