I have two boiler systems. One for the heating of the house, and one for sink/shower hot water.

The boiler for the house will not turn off! It does kick on and off for a duration of time like it should, but the problem is that it shouldn't be kicking on at all anymore.

Thermostat is set at 60, turned off, and even the safety switch on the boiler unit is set to off. But it is STILL kicking on every 20 minutes or so.

It's 77 degrees outside... And 80 inside. I'm not only staying very hot even with air conditioner units going, and my pets aren't comfortable either, but I'm wasting money at this point.

How can I get it to stop! Asap?:

  • 1
    Should have it on its own breaker then.
    – Solar Mike
    Apr 27, 2021 at 19:30
  • 3
    There should be a shutoff valve on the gas supply line, turn it off until repair is done.
    – r13
    Apr 27, 2021 at 19:30
  • 2
    For the system to kick in every 20 minutes or so I would be looking for welded contacts on the controller or thermostat. We will need photos, of the thermostat it could be the issue , fresh batteries if used? For now turn the gas valve to the house heat boiler off if there is no gas it can’t cycle. There should at minimum be a valve to turn it off at the gas valve if not a separate valve before. And photo of all the major components like controller boards, thermostats. That it is cycling makes me think it is more of a controller issue but there may be 2 issues creating problem, battery’s?
    – Ed Beal
    Apr 27, 2021 at 20:07
  • 3
    If the "safety switch" is off and the boiler still fires, the "safety switch" is not wired properly and should be corrected. Meanwhile the gas valve or circuit breaker would be reasonable.
    – Ecnerwal
    Apr 27, 2021 at 20:15
  • 2
    There should be a local disconnect, if so, just turn the damn thing off. If not figure out which breakers or fuses supply that beast and turn them off. If they feed other important circuits, start disconnecting wires to the boiler, cap them and turn the breakers back on. Apr 28, 2021 at 0:03

1 Answer 1


If this is a hydronic heating system using wax zone valves, which act both as water valves and as thermostat, these sometimes fail in the "on" position. If that is the case, disconnect one of the wires from the switch.

That said, as @Ecnerwal states, there is a serious issue with wiring if the boiler still fires with the safety switch "off". Is there perhaps another shut-off switch??

  • The OP has stated it is a gas-fired boiler. See comments directly under the question block.
    – r13
    Apr 27, 2021 at 22:36
  • @r13 -- gas boilers still have control circuits.... Apr 28, 2021 at 0:06
  • @ThreePhaseEel As a gas boiler owner for 20 years, I've never learned I have got a control circuit or breaker. The only thing other than the booster pump that can require electricity maybe is the electronic module that was wired to the thermostat and thermal couple. I don't recall there was another wiring or switch though..
    – r13
    Apr 28, 2021 at 1:02
  • @r13 -- it'd be very odd to find an automatically-controlled gas boiler without one, whether it's powered by a HVAC transformer, directly from mains, or by a thermopile Apr 28, 2021 at 1:05
  • @ThreePhaseEel If it does have electrical parts, then the unit is supper for serving 20 years without any trouble. I don't have HVAC, and as I said, there is no wiring, what is the thermopile?
    – r13
    Apr 28, 2021 at 1:11

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