Pressure relief valve replacement

[B. Phun]

Hi everybody! I just installed this really great wood-fired water heater..in fact, it's so good that it was releasing hot water from the pressure-temperature relief valve within the first 45 minutes of firing it up! In the instructions that came with the water heater it says to replace the valve if it goes off 4 times...well, it went off 4 times within the first couple of hours it was fired up! I don't remember seeing anything on the box the valve came in about this and in searching here I saw one reference from NJtrooper about replacing the valve every 5 years or so--that seems more reasonable to me. So I was just wondering if there's any basis for their idea to replace it after going off only 4 times. Thanks for any input.

[594tough]

If you have a water heater that is so out of control it is lifting the TP repeatedly, then we would expect to see a picture of what is left of your house, on the 6:00 oclock news anyday.


Lifting of the TP is a sign of a serious problem, not a normal operating procedure. I would recommend that you rethink the whole deal.


Holy cow, batman...look at this warning on their website: Not UL listed. Not pressure tested. If not properly used or installed, may explode with life-threatening force.

[dhamblet]

That, in a nutshell, is the problem with this type of unit. You cannot control the heat so if you don't have adequate flow of cool water entering the water in the stove will flash to steam and blow the PRV. The only way I can think of to make this work safer is to install a large storage tank for the heated water or some way to cool the water once it reaches a certain temperature (below boiling point).

[B. Phun]

Thanks for the replies--this unit is installed at a remote cabin that has an unlimited supply of firewood..it's for an outside shower..so far it works really good but I do think the idea of having another tank and setting up some kind of thermosiphon system with this unit would be a better alternative..with a p/t valve on the unit and one on the holding tank...anyway, based on what it says about exploding with life-threatening force, a working p/t valve is a must! That's why I was wondering if they lose effectiveness...

[dhamblet]

You say this is a remote cabin. WHat about plumbing in a waste heat loop similar to a hydronic heating loop? It could be used with an outside radiator and a pump that comes on at say 150 degrees to cool the water back to a safe temp but you would have to also worry about it freezing up at times. Or it could also be used to heat the cabin. But you better find some way to bleed off the excess heat, steam explosions can be ugly. PRVs probably do lose effectiveness over time but it would be popping off earlier rather that later which is a good thing as long as there is a supply of fresh cool water to replenish.