Thermal expansion

jjheat

I have had several customers that were without power for 10 days. Power came back on and their cast iron hot water boilers started up and soon after starting, blew the relief valve and made a mess. I attribute this to cold 40 degree water coming back from several large heating zones. Am I correct??

JStar

Relief

I wouldn't think the cold return would cause this to happen. What kind of expansion tanks are on the system? Do they still have air in them? Was the water main worked on, possibly causing a spike in water pressure?

jjheat

Thermal expansion

But if the whole system and boiler were stone cold wouldnt the feeder have fed some water to maintain pressure loss of the stone cold water??

1 of the systems has extrol 90 that I installed last year on the spirovent before any pumps(pumping away).Water main was not affected at all and has new feeder as well.

JStar

Pressure

If you do some very crude calculations, the pressure could have gone to about 10 psi at 40F. So, it's possible. I didn't think that would be a big enough pressure change to make a difference.