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Munchkin ignoring call for heat

drosner
drosner Member Posts: 53
in THE MAIN WALL

As it always happens was out of town all week when we had single digits in eastern PA and house would barely hold 60 degrees. Called local HVaC service company and the tech took one look at the munchkin and said I should just get a new boiler and he wouldn’t diagnose or touch it.

got home today and the main boiler loop circulator wasn’t running. Dug in more and even when I short the 2 t-stat wires inside the boiler control the boiler doesn’t recognize heat is being called for. Used a multimeter and at least confirmed continuity between the 2 pins on the board that should be closed when any t-stat calls for heat. Yet in the diagnose mode of the munchkin it shows the main circ is off and the boiler won’t go over 150. So it’s just keeping up with the domestics hot water. I hard wired the main circ so at least I’d get 150 through the main zone or two and plan to order a new board on Monday morning.


any suggestions how I can hack this thing so it will keep firing and at least keep water around 150? It’s in the teens next few days so keeping boiler running probably needed anyway. I guess I could remove DHW thermoprobe so the boiler thinks it needs to keep that hot. But will mean super hot domestic hot water…

Comments

  • 109A_5
    109A_5 Member Posts: 2,004

    Warm weather shut off issue ?

    Boiler Model number ?

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • 109A_5
    109A_5 Member Posts: 2,004

    Keep the boiler water flowing through the DHW circuit also. So as when the house cools down the boiler water and the DHW the boiler will fire.

    You could temporarily use house thermostat with a relay to control the main circulator if there is any threat of overheating the house.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • drosner
    drosner Member Posts: 53

    Model is 140 M without the outdoor reset installed.

    I got 150 degree water flowing now but with the house so cold and low 20s outside I’m not getting the house much above 60. So I need to find a way to trick it to raise the upper bound to 180 even if tstat isn’t calling….

    ScottSecor
  • 109A_5
    109A_5 Member Posts: 2,004

    Any Codes ?

    You may only get another 10 degrees from a DHW call.

    image.png

    Is it stuck in a DHW call that never times out ? Was the boiler power down to clear a possible glitch ?

    Is this set correctly ?

    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • drosner
    drosner Member Posts: 53

    great idea…I’ll try to increase DHW to 160 and pull probe out so it’s always calling…

  • 109A_5
    109A_5 Member Posts: 2,004

    If you disconnect the CH thermostat from the boiler is there 24 VAC across the boiler's wires ?

    image.png

    I'm wondering if it is stuck in a DHW call that never times out for some reason, so it simply ignores the thermostat call for heat.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • drosner
    drosner Member Posts: 53

    there should be 24v across the 2 tstat wires going into boiler?


    you are right that if the DHW is calling it will get priority. But I think that is only for a certain period of time. Also the hot water is plenty hot so it’s up to temp.

  • 109A_5
    109A_5 Member Posts: 2,004

    So why has the DHW call not timed out ?

    The thermostat call for heat is just a contact closure (a closed switch), with no thermostat call for heat or the wires disconnected from the boiler the two boiler thermostat wires (boiler side) should have 24 VAC across them. During a thermostat call for heat (contacts closed) the voltage across the wire pair would go to zero.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • 109A_5
    109A_5 Member Posts: 2,004

    I can't speak for Munchkin equipment, but some equipment if the time out timer is set to 0 (zero) it disables it, so it would never time out. In this scenario a stuck DHW call would disable the CH thermostat call forever.

    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,862
    edited January 26

    have you tried disconnecting the DHW thermostat (aquastat) wires to see if that drops out the DHW call and allows the room thermostat to operate the CH circulator ?


    check out my tagline below. After you replace the control board and it does the same thing what will you check next? Perhaps the DHW thermostat! Well…check that first!!!

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • drosner
    drosner Member Posts: 53
    https://forum.heatinghelp.com/discussion/comment/1837873#Comment_1837873

    the DHW is a thermoprobe sensor not a thermostat switch. But I’ll give it a try…DHW has a cycle limit of 30 mins but maybe for some reason the boiler is running it forever and therefore not switching over to the CH mode. In reading the manual carefully the “vision 1” system I have allows for a DHW temperature settings and CH settings and the DHW has priority….

  • PC7060
    PC7060 Member Posts: 1,549
    edited January 26

    Does the Munchkin front display indicate it’s in DHW mode? My newer model HTP displays spiral symbol when in DHW mode and radiator symbol blinks.
    Also @109A_5 mentioned the ODR sensor. If it fails high the boiler will be stuck in warm weather mode and won’t fire the boiler. Check the manual to find the display setting for outside temp. If way out from outside temp the sensor may be bad.

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