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Boiler Temp Keeps Rising

13bravo
13bravo Member Posts: 35
So I’ve had some other posts about replacing my boiler and adding a zone but I wanted to take a step back to what started this journey and pick the collective brain here again:

Back in early part of this year my pipes started thundering like crazy, went down and saw my cg7 WM boiler water temp was pushing 250. Long story short, the boiler heats the house up but when you turn it on the water temp keeps rising, it just won’t stop. I shut her down, it cools down, turn her back on, just keeps right on rising again and in a few hours back pushing 250 and need to cut power off again.

Is this the aquastat? The relay? Something else? Thanks in advance for your thoughts!

Comments

  • HVACNUT
    HVACNUT Member Posts: 5,804
    CG7? The more recent CGa and CGi use a control module. It seems like you needed a pro the first time you noticed it. What's the pressure on the boiler? How old is the relief valve?
  • Jamie Hall
    Jamie Hall Member Posts: 23,168
    This is hot water heat? Not steam? You have a serious control -- and safety -- problem.

    Assuming that this is hot water heat and not steam, the safety valve on your boiler should have released long ago, and put hot water all over your basement. If it didn't, it's defective or installed incorrectly.

    The control problem could be an aquastat. Could be control board. Could be a fired relay in the control.

    Whatever... you should turn the boiler off at the emergency switch, turn the breaker off (or take out the fuse), red tag everything, and not turn anything back on until you both find the control problem -- and get the safety valve replaced.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mikeapolis
  • Zman
    Zman Member Posts: 7,561
    If it wasn't for the thumping sound, I would think you have a bad temp gauge.

    If the temp is accurate, it's sounds like you have a deadly combination of a bad aquastat, high limit and relief valve. Shut it down so you boiler does not end up going through the roof!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    MaxMercy
  • 13bravo
    13bravo Member Posts: 35
    Thanks for all of the comments! It is a hot water system and it is a cg7 (coming on 30yrs old).

    I had shut it down by turning off the power and flipping the gas valve to pilot...I didn't see water anywhere so I am assuming the relief valve didn't work.

    The relief valve, I'm assuming, is at least 15 years old...may have been replaced when the water meter and line were updated. But if not, then it may be as old as the boiler.

    OK, so in addition to aquastat/relay/etc issue I also need a new relief valve is what I'm hearing...
  • Big Ed_4
    Big Ed_4 Member Posts: 2,762
    It could be the aquastat , if you have the cheap L4080 which has the range from 180* - 240* ( Why ???) When they start to go they tend to over ride . Where a L4006A the temperature falls short of it's set point when its starts to fail .When it ever does
    I have enough experience to know , that I dont know it all
  • hot_rod
    hot_rod Member Posts: 22,024
    When boilers get filled with mineral deposits they will often overshoot temperature also. Usually after the burner shuts down, you see the temperature continue to increase.
    You need to see if the burner is on or off when it overshoots.
    Deposits in a boiler can also cause that thumping or percolation sound.
    And it is usually old boilers that take on water continuously.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • 13bravo
    13bravo Member Posts: 35
    Burners seemed to keep going, it didn't appear to be after burners shut off
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Could your gas valve when powered down not be closing completely?
    Could happen sometimes stuck open sometimes closed.
  • mattmia2
    mattmia2 Member Posts: 9,575
    If my math is right the boiling point at 250 f is about 15 psig so it should not have cased a 30 psi relief valve to open.
    rick in Alaska
  • 13bravo
    13bravo Member Posts: 35
    So I had a heating guy take a look and he said definitely aquastat and that the pressure relief valve would not have gone off (to mattmia2's point).

    Is this something an average DIY'er could replace? Does the aquastat penetrate the boiler? Thinking of replacing it with a triple aquastat instead of replacing the boiler.

    Can't really find any online instructions on replacing it, just on replacing the relay.
  • 13bravo
    13bravo Member Posts: 35
    JUGHNE said:

    Could your gas valve when powered down not be closing completely?
    Could happen sometimes stuck open sometimes closed.

    How would I be able to confirm this?
  • JUGHNE
    JUGHNE Member Posts: 11,042
    edited October 2020
    Assuming you can see the burners, when the burners should be off there should be no fire, not even a small one.
    This may not happen all the time, but it is a possibility that the gas valve does not close completely some of the time and boiler continues to heat.
    If this happens with the power off to the valve, you need a new gas valve.......serious situation.
    It is a rarity but does happen.

    If this is the case, then it is the saving grace that the gas is being burned and not just free flowing into the boiler.
  • 13bravo
    13bravo Member Posts: 35
    JUGHNE said:

    Assuming you can see the burners, when the burners should be off there should be no fire, not even a small one.
    This may not happen all the time, but it is a possibility that the gas valve does not close completely some of the time and boiler continues to heat.
    If this happens with the power off to the valve, you need a new gas valve.......serious situation.
    It is a rarity but does happen.

    If this is the case, then it is the saving grace that the gas is being burned and not just free flowing into the boiler.

    So you just mean when the pump turns off and the t-stat isn't sending a heat signal anymore, is that right?
  • mattmia2
    mattmia2 Member Posts: 9,575
    Like you turn the disconnect switch off to the boiler and the burner is still burning.
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Exactly as Matt said. After the boiler is thru with a cycle, then turn the power off. If you look, with the lights off and you in the dark, and see any flame then that is a problem....you may have to lay on the floor.
  • 13bravo
    13bravo Member Posts: 35
    OK, so I turned the boiler on and sent a signal by turning tstat up. The burners lit up as normal, circulator pump started and temp started to increase. At around 175f the burners scaled back to a very low flame...the circulator pump continued and the tstat was still not up to temp. But the water temp continued to rise (assuming because the low flame on the burners) and I shut it all down at 195f.

    So if I am understanding this right, it sounds like the aquastat actually worked, right? I'm assuming it was supposed to turn off the burners completely but a slight flame remained on all of them...is that the gas valve continuing to leak a small amount of gas? The burner flames should have cut out completely, correct?
  • mattmia2
    mattmia2 Member Posts: 9,575
    What do you have to do for the burners to g out completely? You aren't just seeing a single pilot flame are you?
  • 13bravo
    13bravo Member Posts: 35
    edited October 2020
    No, the pilot flame is definitely on but I’m talking about all of the burner tubes on either side of the pilot. They all remain lit but with a very very low flame up and down the length of each burner tube. Is that normal? I assumed they should shut off completely once water temp is reached but I’m not sure.
  • mattmia2
    mattmia2 Member Posts: 9,575
    if you turn the power off do they go out?
  • HVACNUT
    HVACNUT Member Posts: 5,804
    Is it a 2 stage gas valve?
  • 13bravo
    13bravo Member Posts: 35
    edited October 2020
    mattmia2 said:

    if you turn the power off do they go out?

    So I tested again, lowered aquastat to 160 and right around 160 the burners scaled back. When I turned the electrical power off the burners stood lit with that low flame. But when I turned the gas valve from on to pilot those flames went out.

    Two questions:
    1) If the gas valve wasn't complete closing, wouldn't the flame continue even after I turned to pilot?
    2) Could the gas have continued coming because the tstat was continuing to send a signal, regardless of aquastat and power?
  • 13bravo
    13bravo Member Posts: 35
    HVACNUT said:

    Is it a 2 stage gas valve?

    I don't believe so, I don't see any hi-low on it. I believe the P/N is VB00 A 1591
  • JUGHNE
    JUGHNE Member Posts: 11,042
    As said above.......Serious Situation!!........

    You need a new gas valve.
    The standing pilot has been your salvation by burning off this "gas leak".
    When you go to "pilot only" position on the valve you are manually closing the main gas flow.

    Heating guy probably did not look at burners.

    You may as well have burners and pilot burner cleaned with new gas valve and thermocouple replacement.

    Shut off the gas at the valve in the gas piping exterior to the boiler......
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,575
    Also, don't hire whoever left it in that state.

    And as stated above because it is super important, turn off the manual valve, the valve outside the boiler, and the power and don't turn it back on until someone that knows what they are doing fixes it.
  • 13bravo
    13bravo Member Posts: 35
    Freaking nuts! Thanks for the help...gas valve is closed. I'm back to do I replace the near 30yr old boiler or just replace the valve if all else is still working...

    A sincere thank you to all once again!!!
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Concerning a boiler change out, do you have cast iron rads or fin tube convectors?
  • 13bravo
    13bravo Member Posts: 35
    edited October 2020
    JUGHNE said:

    Concerning a boiler change out, do you have cast iron rads or fin tube convectors?

    All but one are convectors...in one room, for some reason, there is a steam style iron radiator. But it is all gas fired hot water, 1 zone, 2 pipe direct return.
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Because of the convectors, you most likely have to run a higher supply temp of water.
    Because of the higher supply temp the return temp will also be relatively high and not able to take full advantage of the condensing nature of new Mod Con boilers.

    Something to consider for boiler change out.
    You may only gain a little more than 10% efficiency by a major up grade to Mod Con and have higher maintainence costs down the road.

    Mod Con parts can easily cost up to $500-600 for main PC board.
    I have one sitting on the shelve to replace seemingly defective.
    As soon as it was delivered the boiler never acted up again.
    If I return the board, then another lock out may happen.
    2-3 days to get replacement......and this is a common component of a common Mod Con boiler.
  • 13bravo
    13bravo Member Posts: 35
    JUGHNE said:

    Because of the convectors, you most likely have to run a higher supply temp of water.
    Because of the higher supply temp the return temp will also be relatively high and not able to take full advantage of the condensing nature of new Mod Con boilers.

    Something to consider for boiler change out.
    You may only gain a little more than 10% efficiency by a major up grade to Mod Con and have higher maintainence costs down the road.

    Mod Con parts can easily cost up to $500-600 for main PC board.
    I have one sitting on the shelve to replace seemingly defective.
    As soon as it was delivered the boiler never acted up again.
    If I return the board, then another lock out may happen.
    2-3 days to get replacement......and this is a common component of a common Mod Con boiler.

    JUGHNE said:

    Because of the convectors, you most likely have to run a higher supply temp of water.
    Because of the higher supply temp the return temp will also be relatively high and not able to take full advantage of the condensing nature of new Mod Con boilers.

    Something to consider for boiler change out.
    You may only gain a little more than 10% efficiency by a major up grade to Mod Con and have higher maintainence costs down the road.

    Mod Con parts can easily cost up to $500-600 for main PC board.
    I have one sitting on the shelve to replace seemingly defective.
    As soon as it was delivered the boiler never acted up again.
    If I return the board, then another lock out may happen.
    2-3 days to get replacement......and this is a common component of a common Mod Con boiler.

    Thanks Jughne, I appreciate the insight. I have read/heard/been told similar things (although with less detail than you provided so thanks for the additional intel).

    In addition to the above you mentioned there are also significant and PIA code hurdles I would have to deal with to direct vent. If I did replace I was going with a standard efficiency model (was considering to go with the current direct replacement (CGA-7-PIDN). My real struggle was do I replace or do I repair. Some say if it isn't leaking and you aren't going to get significant gains in efficiency from an upgrade, just repair...might get another 10 to 20 years out of it.
  • 13bravo
    13bravo Member Posts: 35
    Just to wrap this up, replaced the gas valve, problem gone. Thanks again for everyone's help.
    mattmia2Zmanrick in AlaskaJUGHNE