Water Pressure in Baseboard Heating System Keeps Rising

[skeezix]

I have a baseboard heating system, the kind with a boiler, circulator, a Cash-Acme backflow preventer, and three zone valves. It has been working nicely since 1982 when it was installed. It has a combination pressure and temperature gauge and a water input valve. The pressure should be between 15 and 20 PSI and the temperature has always been 80C.

The backflow preventer (which I've replaced a couple times) has a very, very slow dribble. To stop that I've closed the water inlet valve, making the system a closed system. I've run it that way for several years.

A couple times every year I notice that the pressure is above 20 PSI (even with the inlet valve closed), so I open the drain valve (while the pump is running) to let water out of the system until the pressure drops back to 15 PSI. When I close the valve I can hear something gurgle for a second or two in the boiler. Lately though I have had to open the drain valve more often. I have replaced the pressure reducer valve twice, the last time being around a year ago. Now I check the pressure weekly and even with the inlet valve closed the pressure keeps rising (over a week or so) and I keep letting water out through the drain valve (with the pump running) until the pressure is back down to 15 PSI.

Before I monkey around with the pressure reducer valve I thought I would ask here for suggestions as to what might cause this. I don't think it is the inlet valve.

 

[Diehard]

What type of expansion tank do you have?

Take a picture or two and post them

 

[frodo]

if the pressure is rising with the inlet valve closed. then the inlet valve is leaking through
it is a faulty valve
replace the valve with a watts full port ball valve or a hammond full port

to prove this theory, replace the psi gauge with a tattle tell gauge
https://www.supplyhouse.com/Bluefin...ping&msclkid=1316cd9c6ebf1dd08f7a931cd9b4756c[remove the hose connection, use only the gauge]
this will SHOW you ''creep''
tonight it will be 15psi
tomorrow 17 psi
next week 20 psi

 

[skeezix]

I haven't done anything with the expansion tank since it was first installed in 1982. I don't know what the symptom(s) would be that would warrant a check.

Not much of a picture, but here 'tis...

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I'll put a pressure gauge on the system like Frodo suggested.

 

[Diehard]

I guess the pressure gauge will confirm what you have already noticed with the system pressure rising with time.

Let me ask, do you leave the the shut off valve closed all the time, now?

I'm just wanting to make sure we can rule out the expansion tank having a lack of air to cushion for the expanding water when heated, since that is a common problem for many. But if you never see it drop in pressure, in between uses and you leave the shut off valve closed constantly now, it's likely the valve, as mentioned.

Just out of curiousity, does that expansion tank have a connection to allow adding air(schrader valve)?Or does it have a hose valve?

 

[frodo]

1982?
about time to replace it. I guarantee it is failed and not doing anything
find the schrader valve on the tank and check if it is holding air
if it is not holding air.replace it

 

[skeezix]

@Diehard
I've had the inlet valve closed for years, but just recently the pressure has slowly risen on the heater side of the valve.

I put a new gauge on the drain tap and opened the tap. The pressure rose a tiny bit. So then I opened the inlet valve. Now, 24 hours later, the pressure has stabilized at about 19 PSI. At that pressure, the gauge that came with the heater reads about 26 PSI, so I guess that gauge is just inaccurate.

I closed the drain tap, removed the new gauge from it and put a stopper on the tap. I'll keep a close eye on things for the next week.

The expansion tank is kinda tough to access. It does have a hose bib but I don't know if it has a schroeder valve on it. Hafta check and report back here.

Always sumpthin' to keep things interesting!

 

[Diehard]

The reason I ask about the expansion tank is because there are 2 basic types. The newer versions that include a rubber bladder or a diaphragm that separates the air from the water. These would definitely have a schrader valve that allows you to add air and would not have a drain valve.

The older expansion tanks are just plain steel tanks without a liner but always had a hose end valve to allow you to drain it when such time that too much of the air got absorbed into the water. This would reduce the amount of air in the tank reducing the amount of space required for the hot water to expand to. As a result, the pressure would rise.
These tanks typically have a hose bib to allow you to drain it and a valve that would allow you to isolate from the rest of the system while draining it.

I have the plain steel tank on my heating system and although I haven't had to drain it in a very long time, I have many years ago when the pressure started rising.

So if it was determined that you have the older tank, without the bladder but rather the drainable type, it would be an easy matter of draining it. [Sometimes you can get an idea as to whether it is all water or mostly water by taping the tank. The lower portions should sound rather solid vs the higher portions which would sound more hollow if filled with air.
In any case, draining would cause no harm and would establish its maximum amount of air space for expansion purposes.

 

[frodo]

A tank without a bladder would have a site gauge

that is a glass tube allowing you to see the water level

 

[Diehard]

A tank without a bladder would have a site gauge

that is a glass tube allowing you to see the water level

Some do and many don't. Mine does not.

A gauge would be nice.

 

[Diehard]

Here's mine!

 

[skeezix]

It's now three days after I opened the water inlet valve to the baseboard heating system and left it open. Since then, the pressure has risen from 15 PSI to 25 PSI so I thought it's time to make an adjustment.

My pressure regulator is a Watts #1156F that I bought new and installed last November.

​

I reinstalled my gauge, removed the purge lever and the rod leading down from it. I loosened the lock nut and turned the adjustment screw clockwise until the pressure began to increase. Then while still watching the gauge I turned the adjustment screw counterclockwise four full turns but the pressure remained at 25 PSI and has not decreased. I'm afraid to turn it any farther because I'm afraid it will pop out and I will have a water mess on the pedestal.

What should I do? Are four turns enough to do anything?

 

[Diehard]

Well the pressure wouldn't decrease unless you let it out. Like open the drain valve and allow the pressure to drop to your new setting.

If I were you, I would also drain that expansion tank. Because if it has a drain valve it's not a bladder tank and should be drain completely. I assume it has an isolation valve to shut it off from the system.
If there's nothing else to allow air to enter, just let it gurgle out until plenty. Once it's completely empty, close the drain valve and reopen the isolation valve.

I never asked if you ever notice the pressure rising when the boiler is running.???

 

[skeezix]

@frodo - I'm using a good PSI gauge, connecting it to the boiler drain, and opening the drain valve.

@Diehard
I don't have an isolation valve between the expansion tank and the boiler, and the pressure rises over a period of a few days.

I'll turn the main water inlet valve off and empty the expansion tank when the weather warms up because... I'm thinking that emptying the tank will also lower the water level in everything that's above the tank (like the 2nd floor) and I don't particularly want to monkey around with bleeding the entire system at this time.

 

[Diehard]

@frodo - I'm using a good PSI gauge, connecting it to the boiler drain, and opening the drain valve.

@Diehard
I don't have an isolation valve between the expansion tank and the boiler, and the pressure rises over a period of a few days.

I'll turn the main water inlet valve off and empty the expansion tank when the weather warms up because... I'm thinking that emptying the tank will also lower the water level in everything that's above the tank (like the 2nd floor) and I don't particularly want to monkey around with bleeding the entire system at this time.

It doesn't make any sense to me not to have an isolation valve for an expansion tank that has a draw off valve to drain it.
I don't think I mentioned it but generally you can get an idea if the tank has air in it by knocking/tapping on different levels of the tank. Pretty good difference in sound between where there is water and where there is air.

When you do shut the system down would be a good time to find out if you inlet valve is leaking as was one possibility mentioned.

 

[skeezix]

Thanks for the tip! I did the tap-tap test on the expansion tank a couple months ago and according the the sounds the tapping made, the tank did appear to have air in the upper half.