Home Repair

The pressure valve pops on the hotwater heater

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I have a hotwater heater used as a supply for a radiant floor heating system. The output of the heater has one circulating pump and has an expansion tank and water hammer valve. PROBLEM, A few weeks ago I started it up and all went well, but today , I started it up and after about 45 minutes the pressure valve popped off. Not sure what would be at fault as I have never heard of that type of valve failing. It is clean and does not leak at all under cold water incoming pressure. There is another auto set valve in the incoming line, could that be a pressure limiting valve. Seems odd that hot water would be pumped through the system at inlet water pressure. Furnaces usually are less than 15 pounds. Confused ?
Using the hot water heater for heating up the water is common in the southern states. There should be a backflow preventer then a pressure regulator at the cold water inlet to the system. The regulator also might have an auto feed to keep the system topped off.

This is either faulty or there is some sort of by-pass that you might have overlooked. You are correct that 15 - 20 lbs is the normal operating pressure for forced hot water systems and the pressure valve will pop off at around 40 -50 or so. Cold line pressure might be just under that until you start heating the water. The pressure will build up somewhat higher, fill the expansion tank (if there is one) then goooosh! hot water all over the floor!!

Look for a bypass line that might have been installed or replace the regulator.
Yep, the homeowner had turned on a bypass valve thinking that that was supposed to be done when shutting off and on for the season. Line pressure plus heat drove the pressure high enough to pop the valve.I told them to leave the valve shut off as there was already a low pressure feed to replace water in the line if and when needed.
Glad you figured it out!!


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