Water heater issue

[tbart16]

yeah this is gonna sound easy or even cut and dry ,but its been nothing but a headache.

I have a Nat. Gas bradford white waterheater model m2tw50t6fbn that keeps blowing off the relief valve. The house is equipped with a new pressure reducing valve set at 65 psi I have replaced the relief valve and also the therm ex tank ( the previous one was bad) I added pressure to the new tank so that it equals the incoming house water pressure. The heater releases about 2 gallons of water every other day or so. I am assuming the relief valve is going off on temp since the press is only 65 psi at the heater,but the customer has not noticed any difference in temp the water temp is about 130degrees. any help appreciated thanks Tom

[Caduceus]

Maybe the T&P releases when the burner is firing because the thermostat is not detecting actual temperature until it exceeds limit. If the customer could get an accurate temperature at the time the T&P blows you could confirm this. I have experienced a faulty thermostat that continued to fire the burner and create a similar situation and by the time that I made it to the call, the water had cooled/been used some and showed a lower temperature. I showed the customer how to take the temp when it happened.
Let us know how it turns out.

[LiQuId]

Could be that you have scale or deposits on the inside of the thermal well. this would cause the rod and tube to respond sluggishly and as such the actual temperature rise might be greater than what is detected. turn the temperature up a little when you go there next and step back to see if the TnP blows shortly after firing. if this is the problem then turning the tank up should simulate it nicely. remedy is either a new tank or a cleaning and flushing of the existing one.

- A good way to see if the water is mineral rich is to check around the house at the sinks and check the airators... are they scaled up ? if so then likely this is your problem .

[tbart16]

not really any scale issue at any of the fixtures, Bradford white sent me a new thermal well and a new gas valve just got them today I am gonna install the well first than do the gas valve just for the sake of eliminating one problem at a time thanks for the ideas and the help. I'll keep you posted.

[tbart16]

Fixed! The water heater actually feeds a heat exchanger which shares duct work with the A/C. The A/c is so cold it is actuall circulating cold water through the exchanger back into the the water heater giving it a false temp reading causing the burner to fire on an already hot water heater causing the releif valve to blow. I shut the valves off in the heating loop and it has been dry for a week.

[phishfood]

Thanks for following up. Such a thing had never occurred to me.

[superfitter]

install a check valve on the heating coil loop. then you're problem is solved permanently