Pressure relief valve is always blowing

I am new to the forum, and am very happy to have found a place where I can talk to and learn from some intelligent people on these topics. Most people today are just zombies without brains or the interest to use them if they have them!

My problem: I had installed a Harman 2500 wood/coal hot air furnace and an A.O. Smith power vent LP water heater. A Hilcoil loop was also installed in the furnace. The contractor says he installed everything according to specs and instructions, but the hot water tank pressure relief valve is always blowing. He did put in an expansion tank hoping this would solve the problem, but it didn't.

There are only two adults in the house.

I was told by another contactor that pressure relief valves get stuck all the time especially if they are used a lot - and using well water. If it gets stuck and won't go off, the whole thing will blow up in my basement and I could even have a resulting LP leak too which could cause a fire. Is all this true and/or likely??

Of course, now I am very worried. The contractor is willing to "make the job right", but he is out of ideas. By the way, even though the relief valve blows, the water heater still fires when someone is taking a shower.

I'd rather not put in a section of radiator to draw off the extra heat from the water since there is nowhere nearby that needs the heat and I don't want to waste it.

If I have to, I'll put a circulator in, but I really didn't want to be electric dependant and wouldn't I have to put in much bigger lines to compensate for decrease flow due to the obstruction of the impellors of the circulator when I must depend on gravity to move the water during an outage?

I live in Honeoye, N.Y. near Canandaigua. Can anyone come out and look at my set up?

Thanks. I'll be anxiously awaiting some advice.
Lou

I wouldn't worry about blowing up. It might get hard to see and feel like a sauna, but your relief valve works, no explosion. The fact that your LP heat comes on when you use hot water say's this thing isn't working right. The pressure build up and resulting saftey relief is because the water is not moving through the coil in the stove quickly enough. The temperature rises too fast and the water flashes to steam pressurizing the entire loop. A circulator pump would cure this. If your plumbing is sized to the water heaters ports their size should not be a problem for a circulator. And yes, well water (really the crap that is in it) can make a mess of valves and things. The saftey relief should not stick open after the pressure drops but they often dribble after being exercised.
These coil in stove installations usually have little details that vary install to install, once worked out prove very satisfiying.

Hello Lou, welcome to the forum. I've split your topic off from the other one. You'll get better responses with your own thread.

Hello Lou, welcome to the forum.

The first few thoughts about your problem were: too much heat with too little and infrequent use of the hot water. And second, what coaledsweat said: the water is flashing to steam in the coil due to poor circulation.

After some thought, is the problem pressure, overheating or both?? A watts valve on hot water heater systems relieves at very high temperatures and pressures, so either one or both could be the problem. What is the pressure your water system opperates at? It might be so high that the relief valve only needs a nudge from heat to have it open.

I would consider adding an additional water holding tank or 'conditioning tank' to your system. This additional tank would have the cold water supply feeding it instead of feeding your LP water heater. The water supply to your LP water heater would come from the holding tank.

Adding a circulator is also a good idea, in the event of a power failure, the water would still be able to gravity flow through the circulator, but slower than through just pipe. But the circulator would provide a much faster recovery time for the hot water. And reduce or eliminate the water flashing to steam in the coil.

You are saying that the relief valve blows frequently. Is the water in your LP tank reaching 200*+? or is it not getting hot?? If it is not getting hot, then what coaledsweat said is almost for sure the problem. The system is not thermosiphoning correctly.

If your water is getting really hot and then the relief valve is opening, then you need more capacity, and you need to use up some of the heat somehow that is stored in the tanks. Like a section of radiator like you mentioned. The greater capacity will allow a longer time before the water reaches the temperature blow off threshold.

Let us know what the water temp is in the LP tank. You mention that when taking a shower the LP still fires up. Unless you have a very small LP tank, like 30gal or smaller, or you take 45 minute showers, you should be able to store enough hot water for two 10-15 minute showers.

The least expensive and simplest thing to do would be to add the circulator to the system. See if this improves the system. If it isn't enough and the relief valve still pops off, then a second tank for greater capacity may be needed. If you still have too much hot water, then a section of baseboard to shed some heat is in order.

Hope this helps, Greg L

,

How close is your tank to your stove? 10 feet or less?
Like they said, you may need a circulator pump.

Make sure all your valves are in the correct position for the flow thru your stove.

Maybe you have air in the line, do you have a high point blead valve ?

Have you changed your T/P pressure valve on your hot water tank or how new is it? Is that the one blowing or the one downstream of your stove? Do you have only 1 or 2?

If the valves are older and not used, they can build sediment up and stick open/closed. They recommend excerising them every 6 months - Year.
I tried that once and couldn't get it to reseat and it kept leaking, had to buy a new T/P relief valve.

Thanks to all who replied!

Could my problem be that the installer has the cold water intake coming from the bottom of the hot water heater going straight up about 2ft. , then elbowing out for about 8in, then elbowing straight for about 2ft. and then elbowing in about 8in. into the furnace? Would this account for the water not circulating fast enough in the tank and causing the valve to blow?

Would an elbow at the bottom of the hot water tank angling the pipe diagonally up to the furnace and then elbowing in help?
Thanks,
Lou

I don't think that would change anything really. How big is the tubing, 3/4" or 1"? If it's that big and not moving well you need a pump.

A photo of you piping would be helpful. Another possibility for the pressure relief valve opening would be if your house has an check valve on the cold water line. Some municipal water systems require this to prevent back flow from your house to the mains. The check valve is sometimes an integral part of the water meter. When water is heated it expands. That expansion has to go somewhere. When no hot water faucets are open the only place it can go is outside your home. But it can't do this if there is a functioning check valve. If you are on a private well system with a submersible pump there is an integral check valve in the pump. Get to much pressure build up an you can blow the PVC piping off your well fittings. This is not common because the water normally just backs up into your air bladder water pressure tank. But if the tank is "water logged" it can happen.

Some local plumbing codes require check valves on hot water heaters. In that case a local air diaphragm expansion tank must be installed. Do you have any of the described situations?

Yanche

There should be a check from the well, just prior to the tank too.

I know our street pressure is 85-100psig and then you add in the high temperature of the water and it can easily pop the relief valve, my neighbor had the problem with his boiler/hot water and had to put a regulator on the main line coming into the house to reduce the pressure.

I haven't located the check valve yet, but it seems from what everyone says there must be one somewhere. However, since check valves are necessary, what am I to do about it anyway?

I have a new/old problem!! I woke up this morning and the black pipe from the furnace was stone cold, there was still some coal burning, and when I openned the door, of course, the stench of the coal went in my face. I had to keep lighting paper (with smoke billowing into the room through the closed feed and ash doors) to try to warm up the flue. This has happened once before. What's up with this?

I'm feeling very frustrated.

Lou

You probably have to increase the minimum air to the fire, so that it will create enough heat to keep the chimney drawing. Coal fires can't idle too low or they will go out. A chimney needs warm/hot air in it to draw correctly.

The other item may be that you have a very tight house and there are other fan forced exhaust vents in the house. A clothes dryer, a kitchen fan, a bathroom fan and even your hot water heater all pull air from the house and force it outside Your furnace chimney will reverse flow if it has too much negative draw from the house, overcoming the chimney draft.

Did your installer use a draft gauge to check draft with all the exhaust fans in the house running??

Hope this helps. Greg

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Check the expansion tank elevation, and the height of the pipe at the tank versus the height as it comes off the hot water coil plumbing.

If it is on about the same level, or (worse) lower than the high point in the hot water loop then the tank will tend to get water-bound. Once it fills up with water there is little or no air cushion, and the pressure rise which comes about when the hot water loop gets hot and stays hot will be enough to kick the relief.

I had a similar problem years ago that would typically only occur during periods of heavy demand (like now, with outside temperatures on the order of 5 to 15°F). I could close off the service valve to the expansion tank, drain it, open up the isolation valve again, and the "pressure relief kicking off" symptom would go away for a couple of days or weeks, but eventually return. It didn't happen at all during summer, when the only demand was for hot water.

After about two years of this I dug in, and looked at the system to figure out what was going on.

Didn't see any evidence of air or water leaks from the tank itself (which would also allow a tank to get water bound), but did notice the plumbing
contractor had run the line to the tank on a very slight drop - about 1/8th of an inch over about four feet - between the hot water system and tank. Let the fire go out, drained the system, and replumbed it so the line to the tank was on as much of a rise as I could get (which wasn't much - maybe an inch; other piping was in the way).

Refilled the system, and have only needed to drain the expansion tank twice in the intervening 8 years.