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Pressure problem in older home radiator/furnace

We have a house from the 20s with pretty standard heating system - natural gas furnace in the basement with heated water running through cast iron radiators throughout the house. THe only place that is different is the kitchen which has two toe kick heaters instead that are on the same system. The heater is about 15 years old and in good condition.

The first year we were here we had no problems but this year I am having a really tough time getting the pressure where I need it. The regulator was changed out two years ago but seems to overfill the system. Even with that turned off, I seem to constantly be having to release water (or it comes out the pressure valve on it's own) or add after that. I've bled the system quite a few times and can't figure out why there would be such wide fluctuations. I should add that I also can hear what sounds like water dripping from within the pipes (but can't find drips anywhere) almost as if they are not full and the condensation is dripping back into the water below.

Any thoughts?

Re: Pressure problem in older home radiator/furnace

If the water pressure is increasing with the fill valve off your problem is with the expansion tank. If you have a bladder tank it needs to be replaced. If you have expansion tank that is strapped between the floor joists then it needs draining.


Re: Pressure problem in older home radiator/furnace

We have an expansion tank. Is there any way to check and see if that's the problem, or any other reason why this would be happening?

Re: Pressure problem in older home radiator/furnace

I agree with John.

You have a boiler there Proteus, not a furnace.

You have what's known as a "waterlogged tank"---the ET is ordinarily 1/2 filled with air & 1/2 with water to act as a cushion, over time the air tends to get absorbed by the water & the tank becomes waterlogged--the pressure relief valve, near the boiler is rated to open at 30 psi, spilling water on the floor, as a safety device to protect the boiler & the piping.

When you say you have an "expansion tank", I assume you mean, as John said, that you have a 3' steel tank (usually green) strapped to the boiler room ceiling joists.

The way hot water boiler systems work is that they heat the water inside the boiler & piping system---since water EXPANDS about 4% when it is heated, this expanded water will crack the pipes & boiler, unless there is a tank with an air pocket that will compensate for the increased volume of water---as long as the tank is 1/2 filled with air, it will act as a cushion for the increased volume of water.

You have to temporarily shut off the boiler at the power switch, then shut off the faucet on the pipe that leads to the expansion tank (isolating valve); connect a hose to the faucet valve of the ET, direct it to a nearby drain or barrel & open the ET faucet to allow the tank to drain all its water---there is usually a little air valve near the faucet you have to loosen to allow air in the tank for a better drain.

Once all the water drains out, re-close the air valve (if present), re-close the tank faucet & reopen the faucet that leads to the ET (isolating valve) ---this will preserve an air pocket in the tank, & allow water to flow into the ET until it reaches the needed 12 psi pressure (you will hear water flowing to the ET); switch on the boiler power switch when the boiler gauge reads at least 7 psi.

After you solve the expansion tank deal, you'll have to go around to the bleed valves on the radiators & bleed the air out of the system, especially any rads that are higher up, on the 2nd floor, etc.---whenever you add new water to the boiler system it contains entrained air that eventually separates from the heated water & makes for "noisy pipes" until you bleed the air out---take a small screwdriver & small cup to catch any water that comes out; the small bleed valves can be found on either end of the rads.

The site below charts the steps to follow in draining the ET, and has a diagram of the valves & components involved.


Re: Pressure problem in older home radiator/furnace

OK, just took a look and the expansion tank is the Extrol Model 60 which doesn't seem to have a drain valve but does seem to have a bicylce pump type air valve on the bottom. From the feel of it it seems to be empty but not sure if that's accurate. So it doesn't really look like it's the kind i can drain. Any thoughts?

Re: Pressure problem in older home radiator/furnace

The Extrol Model 60 is a bladder-type ET which holds close to 8 gal of water, & would weigh close to 80 lbs, if indeed it is waterlogged, in which case I recommend you don't try to service this yourself, but call a service person; do you have any photos you can upload.

The boiler & its associated piping all operate on a low pressure---12-20 psi, as a safety measure---but the boiler/piping is surrounded by nearby piping & components that operate at "house pressure" of approx 50-60 psi---if any of these components become bad, they will leak into the low pressure boiler/piping & quickly raise the pressure above 30 psi, at which time the pressure relief valve opens & spills water on the floor.

For a simple check, if you can access the "bicycle-type air valve" on the bottom of the ET (there's usually a little plastic cover that can be removed) & press your thumbnail momentarily into the "tire valve". If you get any water on your thumb, the tank is waterlogged & has to be replaced.

Other possibilities could be that the pressure REDUCING valve (which is on the water supply line) is dirty or shot & is allowing high-pressure water in from the 50 psi house water supply line. You can try shutting off the house supply valve (which is located before the PRV) to see if the water pressure stabilizes.

How do you obtain your domestic hot water (DHW) (the water you use for showers, dishwashing, etc.)??? If you have an indirect hot water heater tank next to the boiler, this could have sprung an internal leak & is allowing 50 psi (house pressure) water into the boiler/piping, which ordinarily operates at 12 psi.

If you have a "tankless coil" inside the boiler as a means to obtain your DHW, this also could have sprung an internal leak, with the same effect.

In both cases, the strategy is to isolate these components from the rest of the system using their associated shut off valves to find the defective component---in these cases as well, you would need a pro to come in to make the repair.


Re: Pressure problem in older home radiator/furnace

I'd love to post a pic but can't get it small enough to post up here. Their specs are very strange for pics. I can send if you have an email or post somewhere if that's easier. To answer a couple of questions, I have the water coming into the pressure valve on the inlet side of the system turned off and have for a while because my concern was that this was faulty (it had been replaced) and that was the problem. The system turns on and slowly rises to 40 psi or so and then the outlet pressure reg kicks in and flows out on the floor. So there is no water being fed into the system from the "normal" means when this happens.

We have a separate hot water heater from this system so that doesn't seem like it would be a problem. Meaning usable hot water for the house that is.

I let a quick shot of air out of the bladder and it was all air and nothing else so doesn't seem to be water logged. Also, the tank feels empty when the problems arise.

Re: Pressure problem in older home radiator/furnace


Don't make the mistake of assuming the ET is "empty" by the way it "feels"---too many people have been physically injured assuming this.

Regardless of what component is causing the problem, it's not something on which you should be trying to make a diy fix.

Have you noticed what the boiler gauge is reading when the pressure RELIEF valve is opening & dumping water on the floor???

If the pressure relief valve is dumping water water on the floor & the PRV is reading only 15-20 psi & BEFORE the boiler gauge hits 30 psi, then the pressure relief valve is faulty.

Otherwise, I'm stumped. And we could be missing something that a service person coming into the house can see by actually LOOKING at the system (something we can't do over the internet).

For example, the boiler may have been originally delivered with what's known as a "tankless coil", that didn't deliver enough hot tap water, that 15 years down the road is no longer used, but is still hooked up & is now leaking---who knows.

You may have zone valves on the system that are not opening because one or two of them are bad, or partially stuck, causing the boiler pressure to rise----who knows-----we'd love to eventually know what it was that caused the problem when the enigma is solved, if you can post back.

Again, you need an on the spot service person.

Re: Pressure problem in older home radiator/furnace

Gas co rep just came (we have a service plan my wife bought I didn't know about). He didn't run the system but looked at the standing pressure (10 PSI) and heard what i had to say about what was happening. Apparently we have very large main pipes in the house so his feeling is that we need an additional or larger expansion tank. My question is that the first year we lived here there didn't seem to be a problem but now there is. Is it possible that this could be a problem considering nothng else has changed?

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