520 Boiler Pressure Rising

I searched the forums but without success.
The boiler pressure on my EFM 520 wants to increase until the relief valve starts dripping (20-25#).
I have drained water from the system to bring the pressure down to 10#, but it goes back up within several days.

Is this the domestic water coil leaking into the boiler - or are there other causes?

Inherited Axeman 130 wrote:Is this the domestic water coil leaking into the boiler - or are there other causes?

It could be, or it could be that the bladder in your expansion tank is shot (has a hold in it).

Shut the domestic off and see what happens. If it still builds pressure it is probably the PRV. Well water can eat them up.

No bladder in tank.
City water.

What is the house domestic water pressure? If significantly higher than 26#, I would think it not the coil as it would continue to rise above the 26# you said it stops at. PRVs shouldn't be dripping, I'm venturing a guess that that is the culprit. I'm on well water and my third PRV in 23 years.

If you don't have a bladder type expansion tank, it might be time to check that it isn't full.

At any rate, if your problem is pressure rise while the boiler temp is going up, then it's an expansion tank issue. If the pressure is rising just over time, domestic water pressure is leaking into your boiler (DHW coil).

If the PRV is starting to leak at 25 PSI, it is probably time to change that also. Probably unrelated though.

-Don

If it were my EFM, I would replace the Fill valve, PRV, and bladder expansion tank. then write the date on all 3.

Do you have an auto fill valve? I fill my system to 12 pounds then turn the fill off. If you are having problems after that, then you have a bigger problem.

Shut the water supply off to the PRV and return the pressure to normal. If the pressure stops rising, that's it.

Good Morning Inherited Axeman,

I can offer what has happened to me which is exactly what has happened to you.

What the kind folks here are describing is a "water logged condition " in your steel expansion tank;
wherein the air cushion in the upper third of the tanks volume is gone and replaced with water.

Is your steel expansion tank equipped with a water level gauge??

I/we need to know whether you have an airtrol valve in the steel expansion tank.

The airtrol valve controls the flow of air bubbles in to the steel expansion tank and
holds any air bubbles and the cold water in the tank absorbs the air bubbles and
then the cold water eventually travels back down the airtrol valves cold side and
back in to the boiler steam jacket.

NOW; whats happened is that the water fill valve has allowed the system to refill because of the changes in pressure in the system due to the circulator(s) running and stopping.

You need to shut the fill valve off and keep it shut off then drain the steel expansion tank off to create a one third air/two thirds water ratio again for the system to operate properly.

As mentioned you also need to shut the feed water off for the domestic coil to verify that it is not leaking as well in searching for the cause of the water logged tank condition "after" you have returned the steel expansion tanks water to air ration back to 2/3 water 1/3 air to allow the system to operate properly and have a point of no pressure change.

As mentioned also the Pressure Relief Valve may also be faulty and needs to be replaced.

If your steel expansion tank doe's not have an airtrol valve you should have one installed so your system can operate properly and also avoid having the water logged tank condition "after" you shut the fill valve off.
Once your system is filled you will only need to add water back if there is a leak or you need to change a valve or circulator.

The water fill valve is always closed (off).

Is your expansion tank flooded?

If the fill valve is always closed the
domestic hot water coil has a hole in it.
That is unless you have a boiler fill valve
that is a "Globe Valve" that may be bypassing
if it is not seating properly.

Replaced domestic hot water coil - issue solved.

Inherited Axeman 130 wrote:Replaced domestic hot water coil - issue solved.

Glad to hear you got it fixed and thank you for updating your thread.