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Weil-McLain CGa 5 series 1 won't refire burners until boiler temp drop to 85F

saschwarz
saschwarz Member Posts: 8
edited May 1 in Domestic Hot Water
Hi,

I have a Weil-McLain CGA-5-SPDN boiler that often will fire the burners until the high temperature cutoff temp is reached (180F) but won't refire the burners until the water temp drops all the way down to 85F (as long as the wall thermostat is still requesting heat). The circulator pump continues to run the whole time.

I'm guessing that the aquastat isn't resetting correctly?

Two other things that might(?) have an impact are:
1. The system has a leak that I can't find, copper piping runs through a concrete slab and I'm afraid it is leaking in there. The pressure will drop down to 5-10 psi, I manually refill to 20 psi every week. There are very few air release valves in the system and the highest radiator will often has some air in it. Could there be air trapped in the boiler that would impact the aquastat's temperature sensor.
2. The system has two zones and when the system is in this weird state (water temp ~90-120F - only one circulator running and it's thermostat requesting heat) if I turn up the thermostat in the second zone (not already requesting heat) I hear the relay for it's circulator close/circulator run and within seconds the vent damper opens and the burners fire. Checking the water temp gauge the temperature doesn't change noticeably (so I don't think the second zone is dumping cold water into the boiler) but maybe the electrical load changes in some way to cause the burners to fire??

I'd appreciate any suggestions for debugging this.
Steve

p.s. Sorry it looks like I put this post in the wrong category...

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,157
    I am guessing you have air in the system causing some issues. You're going to have to address that leak.

    Can you post some pictures of the boiler and piping around it?
    saschwarz
  • Jersey2
    Jersey2 Member Posts: 106
    I think it is working normally. When you turn the 2nd zone on, all the cold water rushing into the boiler cools it and the burner kicks on again. The radiators stay very hot, right? The leak you have to get fixed, and it sounds like your water feeder isn't working and needs replacing.
    I'm not a plumber or hvac man and my thoughts in comments are purely for conversation.
    saschwarz
  • Jamie Hall
    Jamie Hall Member Posts: 19,156
    A perhaps obvious question: is it always the same zone involved when the system does this? And what is the complete control scheme? You mention a thermostat and a circulator -- and a relay. What controls what, and how?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUTsaschwarz
  • fentonc
    fentonc Member Posts: 109
    I have that same boiler, but the spark-fired version - here is the manual for it with a troubleshooting flowchart.

    It almost sounds like only one of the zones is actually calling for heat to the boiler. On mine, there is the single Taco 007 circulator that it comes with, and then the thermostats for each zone are wired to zone valves, with the end-switches for the zone valves all wired in parallel. The thermostats just open the zone valves, and then if any of the zone valves are fully open, the end-switch tells the boiler to run the circulator and let the aquastat control the water temperature (which fires until it reaches the high limit, and then falls 20F before firing again).

    Mine was installed in 2016, and the control board for it also has nice status LEDs showing you what state it's in (along with some big 7-segment displays showing you the water temp it's seeing).
    saschwarz
  • saschwarz
    saschwarz Member Posts: 8
    @Jamie Hall Zone 1 (the whole house) is always the zone requesting heat. Zone 2 only heats a converted 3 season room. Each zone has its own thermostat, circulator pump, and relay for activating its pump.

    @Jersey2 when its in this state the radiators in both zones are barely above room temp (60-70F) since the water is only at 80-90F. But, zone 1's thermostat will have been requesting heat for a long time (over an hour) since the air temp will be 65F and the thermostat is set for 70F. This most often happens in the AM when the 62F overnight thermostat setting changes to 70F. So the boiler went from room temp all the way up to 180F and circulated through zone 1 for several hours until the water temp drops down to 80-90F and eventually the burner turns on again since the air temp is still below the requested 70F.

    The auto fill does work but I have closed the valve after it to see if I can figure out how much water is leaking. I open the value when the pressure gets too low. I watch it every day.

    @EBEBRATT-Ed I've attached two photos. The green arrow is the fill line. The green circle is one of the air release valves, I've never gotten any air out of it when I open it.

    Shouldn't I be able to put an ohm meter across the aquastat terminals and detect if it is open/closed? Does anyone know what low temp it normally should close at? 160F?


  • saschwarz
    saschwarz Member Posts: 8
    @fentonc Yes in this case only one zone is requesting heat. I've added a comment above/photos. Each zone has its own pump/thermostat/control relay. Unfortunately, no fancy readouts on this 10 yr old unit.

    I'm going to electrically test the aquastat and see what temp it is closing at.
  • fentonc
    fentonc Member Posts: 109
    Is there a control board behind the front panel? Mine is visible through an open slot at the top of the front panel, but the panel just slides up a little and is easy to remove. Mine has lots of useful state LEDs so you can see exactly what the boiler thinks is going on.
  • saschwarz
    saschwarz Member Posts: 8
    @fentonc nope, just aquastat, transformer, gas valve.
  • saschwarz
    saschwarz Member Posts: 8
    Zone 1 was still requesting heat, circulator pump running, boiler water temp 90F and I figured I should be able to put a jumper across the terminals of the aquastat and then the burners should fire... and they didn't. So now I'm really confused.
  • GGross
    GGross Member Posts: 193
    perhaps a safety is locking you out? What is the status of the low water cutoff?
    saschwarz
  • Jamie Hall
    Jamie Hall Member Posts: 19,156
    Zone 1 has a relay which is supposed to close to request the burner on? Have you checked that relay and all the related connections?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 5,751

    Zone 1 has a relay which is supposed to close to request the burner on? Have you checked that relay and all the related connections?

    This. I think both the controls for your circulators each have a contact 120v for the circualtor and another 24v contact connected to the thermostat connection on the boiler itself to call for the boiler to fire. I think this contact is bad or one of the wires is disconnected on the zone that doesn't fire the boiler with a heat call. If this contact isn't closed, it is in series with the aquastat so it won't fire the boiler if you jumper the aquastat unless you also jumper the thermostat connection.
    saschwarz
  • Jersey2
    Jersey2 Member Posts: 106
    Ohhh, yes 85 is way too low a temperature to trigger the burner. Intuitively I would say the aquastat is bad, but your test has eliminated that as the bad component.
    I'm not a plumber or hvac man and my thoughts in comments are purely for conversation.
  • pedmec
    pedmec Member Posts: 220
    sounds like one of the switching relays was not wired to the boiler circuit. normally 5-6 is switching low voltage burner circuit. just remove the covers and see if the low voltage wiring is on both switching relay 5-6 terminals. 3-4 is normally circulator dry contacts. although they are interchangeable
  • saschwarz
    saschwarz Member Posts: 8
    edited May 6
    @mattmia2 @pedmec Thanks! I didn't realize the relays controlling each pump also had a contact that closed the circuit for the burner. I pulled the covers off of the relay boxes each zone has a Honeywell RA832A:



    The low voltage circuit for the burners is connected across the X X terminals.

    If I short across the T and T terminals on Zone 1 (the zone that only runs the pump and doesn't fire the burners) the relay closes and the circulator runs and the burners fire. That's as I'd expect.

    BUT, if I remove the jumper and raise the thermostat request temperature the relay also closes but only the circulator pump runs. The burners don't fire. Interestingly if I then short across the T and T terminals the burners still don't fire (the boiler water is at room temperature throughout).

    I'm thinking the contacts in the relay for the T T circuit are dirty/failing. That zone cycles much for frequently than zone 2. I'll play around with it some more.
  • saschwarz
    saschwarz Member Posts: 8
    edited May 6
    After more thought, jumpering TT after the relay is closed shouldn't have done anything... duh!

    It seems every time I manually jumper TT the contacts close correctly and the XX circuit closes. But, not when the thermostat completes the TT circuit, then only the pump circuit closes.

    I think I'll switch the thermostat wires from zone 1 to the TT connections on zone 2 and vice versa and that should tell me if their is some weird issue with the thermostat or if the problem stays with the zone 1 relay.
  • mattmia2
    mattmia2 Member Posts: 5,751
    You can short x x on the zone that isn't firing the burner and see if the burner then fires. You can also measure across them with an ac voltmeter. If the relay is good you should measure around 0 v across them when the relay is closed, it you measure several volts or more then the relay is bad.
    saschwarz
  • saschwarz
    saschwarz Member Posts: 8
    @mattmia2 thanks for you detailed debugging help! When the relay closes I'm getting 24V across x x and if I short across x x manually the burner lights. I'll order a new relay unit.
    mattmia2
  • pedmec
    pedmec Member Posts: 220
    sorry for the incorrect terminal numbers. couldn't tell the relay by the pics. just assumed it was the ra845 (no **** joke guys, lol). your contact points are most likely not making contact in the relay. its a mechanical switch and becomes out of alignment. common issue along with pitting of the contacts. replace switching relay
    saschwarz