Recent intermittent pressure increases hydronic boiler.

[Loueber]

Hi everyone, need your thoughts regarding increase in pressure in my hydronic system as of lately, setting off my 30# release valve.
Boiler specs:
McClain early 90s natural gas, ~50gallon cast iron boiler, connected to cast iron baseboards in 1800 SQF house.
boiler water temps set to 190 and 170. (using a infrared thermometer, i can confirm that the water immediately exiting the boilers never gets over 195 and the temp gauge on the boiler itself never goes over 190 either)

Issue: periodically the pressure in the system climbs to 31PSI , which triggers the 30# pressure release valve.

Issue started last year. Which was solved (so i thought) by replacing the previously installed expansion tank with an extrol Ex-30 (
Prior to that i replaced the water feed line valve which was set from factory at 15pounds.)
After that, there was no issue in 2021.

This winter, the same symptoms occur. once in a while, ( seems like its only in the mornings when house recovers from overnight setback) that the pressure builds to 31# setting off the release valve.
Once the house is back up to daytime temps, the pressure on the boiler stays at a steady 25-28#.

at the install of the expansion tank , i initially pressurized it to the incoming water pressure. 15#.
i can confirm that the water pressure regulator is working properly because when the boiler cools down, pressure drops to 15 pounds. So i know the valve is working properly. ( i have also shut off the inlet water feed to test just in case)
Obviously since the pressure is going above 15# when the heat runs, the expansion tank is getting water logged.
So i increased pressure in the expansion tank each day to see if it would solve my issues. Currently im up to 25# in the expansion tank. Which, is pointless since the boiler pressure is getting to 31. So its still getting water logged.

These are my thoughts, and please let me know what you think.
Even though the system has been fine for years with the current set up ( at least so i think) , i was debating on removing the ex-30 expansion tank, and replacing it with a Ex-60 or larger. And setting the expansion tank pressure to 20-25 pounds?
My thought is that a larger expansion tank will provide more room for expansion and the pressure wont raise up to the 30#?
Why this started happening last year is beyond me. the only thing i can assume is:
1- the original ex30 is was not the appropriate size to begin.
2- 190 is too high for the hi-temp setting? even though water temp at pipe exit doesnt get over 195
3- rust build up in the boiler making the ~50 gallon tank a smaller boiler, but that shouldn't matter i dont think, that means the flame would just cycle on and off more.
4- a defective new ex-30? i CAN feel the temp on the expansion tank change as the pressure increases. and cool down when the system drops back to 15# so it SEEMS like it is working. (infra red thermometer confirms change in temp on ex tank) however, being set to 20# and the system hitting 30# then obviously its water logged after 20.

I also ensured the ex-30 and the lines were properly bled and there is no air trapped in the system.

here are some pics because its always nice to see pictures.
thanks!

 

[GrumpyPlumber]

The pressure tank should be 12 psi, pressurizing it to 25 makes it worse.

If the problem recurs at 12 psi, then drop boiler pressure to 13, no less than 12 psi, where your gauge reads 31 at max then a simple drop of 1 psi "might" be enough (the gauge shouldn't read more than 30 psi because the relief kicks at 30).

Also, temp should be 180.

 

[Sponsor]

 

[John Gayewski]

70 degree water going to 195 is 125 difference. At 50 gal of water that should only make about 1.5 gal of extra water once it's expanded. Though I haven't looked up what your model holds, it sounds like your expansion tank is probably big enough to hold 1.5 gal of water. Is it?

If so, and the no sign of it being broken I. e. water coming from the schrader valve, then I agree your starting pressure is too high. Dial it down.

Are you pumping away from the expansion tank and boiler? If not this can cause high pressure at the boiler with lower pressure in the piping where you actually want it.

 

[Loueber]

The pressure tank should be 12 psi, pressurizing it to 25 makes it worse.

If the problem recurs at 12 psi, then drop boiler pressure to 13, no less than 12 psi, where your gauge reads 31 at max then a simple drop of 1 psi "might" be enough (the gauge shouldn't read more than 30 psi because the relief kicks at 30).

Also, temp should be 180.

Water inlet pressure is 15, so wouldn't dropping the expansion tank pressure to 12 , immediately make it water logged?
water temp is set at 190 high, and 170 low. i will reduce to 180 and 160.

 

[Loueber]

70 degree water going to 195 is 125 difference. At 50 gal of water that should only make about 1.5 gal of extra water once it's expanded. Though I haven't looked up what your model holds, it sounds like your expansion tank is probably big enough to hold 1.5 gal of water. Is it?

If so, and the no sign of it being broken I. e. water coming from the schrader valve, then I agree your starting pressure is too high. Dial it down.

Are you pumping away from the expansion tank and boiler? If not this can cause high pressure at the boiler with lower pressure in the piping where you actually want it.

170 on low setting, not 70.
the ex-30 expansion tank lists at "4.4 gallons" so it should surely hold 1.5 gallons of water.
no signs of leaks, and valve is good.
the tank exp. tank is connected to a 1/2 pipe going down into the boiler housing. it doesnt appear to be on the pressure side of the system, and might be as you mentioned, on the return side of the system. it seemes to be installed at the proper location and was done at original system installation. However, i will see if i can determine exactly where its piped to and confirm that.

 

[GrumpyPlumber]

Water inlet pressure is 15, so wouldn't dropping the expansion tank pressure to 12 , immediately make it water logged?
water temp is set at 190 high, and 170 low. i will reduce to 180 and 160.

Max 180 will reduce expansion vs 195, hydronic boilers are made to function @ 180.

For the expansion tank, 12 psi is factory setting, will match the surrounding cold pressure, the higher the pressure, the more resistance to expansion, 25 psi means it won't start expanding until your pressure is at 25.

You can also tell if it's water logged by flicking it with your finger at the top, then bottom and doing it while moving up or down, you'll hear a slight ring or different tone until you get to the water level of the tank.

Water logged tanks have a dull sound from top to bottom.

 

[Fitter30]

From the bottom of boiler to the highest water level what is the height?

 

[John Gayewski]

Reducing the expansion tank pressure will help, but you set the system pressure at the fill valve. Turn that down.

170 on low setting, not 70.
the ex-30 expansion tank lists at "4.4 gallons" so it should surely hold 1.5 gallons of water.
no signs of leaks, and valve is good.
the tank exp. tank is connected to a 1/2 pipe going down into the boiler housing. it doesnt appear to be on the pressure side of the system, and might be as you mentioned, on the return side of the system. it seemes to be installed at the proper location and was done at original system installation. However, i will see if i can determine exactly where its piped to and confirm that.

Don't worry about where it was originally. The boiler manufacturers packaged those boilers so they would all fit (circulator and all) in one package. Which means they incorrectly would put them on the return side. Which is again, incorrect. There's a whole book written about this because the people who get called to fix them were sick of having to explain this or defend it. A conventional boiler should be piped with the circulator pumping away from the expansion tanks and accept the hottest water the system provides.

 

[Loueber]

Max 180 will reduce expansion vs 195, hydronic boilers are made to function @ 180.

For the expansion tank, 12 psi is factory setting, will match the surrounding cold pressure, the higher the pressure, the more resistance to expansion, 25 psi means it won't start expanding until your pressure is at 25.

You can also tell if it's water logged by flicking it with your finger at the top, then bottom and doing it while moving up or down, you'll hear a slight ring or different tone until you get to the water level of the tank.

Water logged tanks have a dull sound from top to bottom.

i dropped the max temp down. hopefully that will solve the problem. Ill know tonight.
ill also drop the psi down as well. it "sounds' like it is water logged, but not too sure. Im more assuming that it is, if its set at 20 and and the release valve is releasing at 30. but itspossible it might not be water logged.

 

[Loueber]

From the bottom of boiler to the highest water level what is the height?

bottom of boiler to highest water level ( first floor baseboard) is 8feet

 

[Loueber]

Reducing the expansion tank pressure will help, but you set the system pressure at the fill valve. Turn that down.

Don't worry about where it was originally. The boiler manufacturers packaged those boilers so they would all fit (circulator and all) in one package. Which means they incorrectly would put them on the return side. Which is again, incorrect. There's a whole book written about this because the people who get called to fix them were sick of having to explain this or defend it. A conventional boiler should be piped with the circulator pumping away from the expansion tanks and accept the hottest water the system provides.

wow interesting point. So i looked and the expansion tank seems to be pipped right into the top of the boiler itself. On the left side. Which is also the same side the return line enters (at the bottom) which is also where the circulator pump is located.

 

[Fitter30]

bottom of boiler to highest water level ( first floor baseboard) is 8feet

10 - 12 lbs is more that enough system pressure with pump off and boiler temp below 100°. Expansion tank pressure then can be adjusted. There is plastic cap opposite piping remove the cap there's a tire valve stem with a low pressure tire gauge check pressure if water comes out tank is bad. Adjust to same as boiler if you need to add pressure use a bicycle tire pump not a compressor. Don't want to rupture the bladder. Take a few pics of the pump, ex tank, related piping and flue so we can how its piped. Bet your basement is nice and warm with so much of the boiler exposed. Do you need 195° to heat the house?

 

[Loueber]

10 - 12 lbs is more that enough system pressure with pump off and boiler temp below 100°. Expansion tank pressure then can be adjusted. There is plastic cap opposite piping remove the cap there's a tire valve stem with a low pressure tire gauge check pressure if water comes out tank is bad. Adjust to same as boiler if you need to add pressure use a bicycle tire pump not a compressor. Don't want to rupture the bladder. Take a few pics of the pump, ex tank, related piping and flue so we can how its piped. Bet your basement is nice and warm with so much of the boiler exposed. Do you need 195° to heat the house?

basement is very warm. lol ok i adjusted temps and pressures as recommended. i did notice something odd going on with the system/thermostat. i will post that on its own vs replying directly to you. But i need to experiment today to confirm what i am suspecting is happening, either in addition to this current problem, or perhaps is the cause of the current problem.
Ok i wont keep you in suspense as im sure your dying to know... i swear that my circulator pump was running whenever the low side adjustment was turning the furnace on. regardless that my thermostat was NOT calling for heat.
this am my baseboards were HOT, even though the thermostat was not calling for heat. went to the basement, and sure enough the circulator pump was running. out of curiosity i turned up the low side setting ti turned down the low side setting to 140, and the pump and furnace turned off. I turned it back to 160 and the furnace kicked on AND the circulator pump started running again.
So im deducing that either the aquastat relay is bad or the thermostat is bad and is calling for heat all the time even though its not set high enough to call for heat.
i dont THINK that would cause i higher pressure in the system. in my mind to me its just making my 50 gallon boiler turn into a 60 gallon boiler and keeping my baseboards always at 160.

so this has either turned into TWO problems, or, the aquastat is bad which is causing both the high pressure and constant pump circulation.

for the record, i have a smart ecobee thermostat. so i know how they can go bad. Tonight i will switch it out with another and see if the same situation happens .