Boiler Intermittently not firing up on call for Heat

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ClFrank13

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I have a Slantfin Sentinel SE 140 (gas boiler) with a Honeywell L8148E 1273 aquastat that I had no issues with sine installed 15 year ago.

My system has 2 zones, in one of my heating zones when there is a call for heat it intermittently fails to fire up the boiler - if that zone does fail, the zone valve opens but the boiler wont fire up unless I do a power cycle to the boiler or lower the temperature on the thermostat below the set point and then raise it back up. This only happens in that one zone - the two zones share the same circulator pump and the circulator pump won't kick on either if that zone fails (unless the other zone id cal;ling for heat).

After doing some research, I understand this specific aquastat is very flaky - and figured I start by replacing that but since it only happens in the one zone intermittently, I am curious if anyone has suggestions on what else to look for. I verified it s not the thermostat because I switched the stats to the two zones and the problem stays with the same zone.

Thanks in advance

Cliff
 

Fitter30

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Honeywell aquastat looks like it has a open relay. If the relay is pulled in should make boiler contacts to start boiler. Having to turn thermostat down and then back up boiler seems to have a signal but has failed to lite and locked itself out. Does your your boiler have a ignition module? Take a pic of the wiring diagram and module if it has one.
 

ClFrank13

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Honeywell aquastat looks like it has a open relay. If the relay is pulled in should make boiler contacts to start boiler. Having to turn thermostat down and then back up boiler seems to have a signal but has failed to lite and locked itself out. Does your your boiler have a ignition module? Take a pic of the wiring diagram and module if it has one.

Thanks for the response. It has a standing pilot - no ignition module.
 

Fitter30

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Screenshot_2021-01-30-15-07-39.png Flue damper open thermostat is calling check roll out and vent switches. Meter gas valve th terminal check both safeties for 24 volts
 

ClFrank13

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If you don't want to replace zone valve just wire in a relay powered by valve.

Thanks for all your responses... it must have been a faulty connection of the zone valve wasn't triggering the end switch - after removing and re-tightening all the wire nuts last week, its been working fine... Thanks again!
 
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