The only thing that will fire the boiler when it is off at the programmer is the frost stat. It'll run the CH for 5 minutes, then turn off for 5 minutes, repeat. Be very careful if your boiler is outside and you are turning it off at the fused spur. The vaporstat is cutting off the boiler but it keeps cycling on. I replaced the thermostat to no avail. Even if I turn the thermostat off, the boiler keeps running. The pump may be getting a live feed from the programmer. The pressure was 27 psi and the water temp was only 100 degrees. This issue has been going on for sometime but gradually getting worse (pump runs for longer and longer). Called a plumber who removed the electric valve to the central heating which I am sure is not the problem as it only controls whether the water goes round the heating circuit. Boiler is about 5 years old as is the thermostat. Is it normal for a boiler system to run for 3-5 minutes or so and then shut off for a minute or two and start back up again? I set the wall controls so that the heating would only come on if it was below 22 degrees (which it hasn't been yet) but noticed that the boiler is constantly making a noise. To get the pump to stop going I have to turn off the boiler at the mains. Turned the heating on today for an hour, worked well, then noticed that well after the hour was up and the programmer switched off, the boiler (Ideal ICOS HE15) was still running, with a call for heat. The pressure didn’t appear to go down at all before the unit came back on… The system should be checked to determine what is powering the boiler and pump, it could be any of these components. I am wondering whether it is the Honeywell aquastat controller.I have model L4080b on the boiler. Even when you shut off the heat at the programmable thermostat the boiler keeps running. Vaillant boiler firing up when heating is off I've moved into a new flat that has a vaillant boiler. Hi , OK ,helps now have the model of your boiler. :help:I have a two zone Smith GB100W gas boiler that still runs after the thermostat has reached the desired temp. My boiler does a similar thing. Turning the room stat made no difference and there was no clicking. Can you tell me the model of your programmer, if you have a room stat , a hot water cylinder stat and if you have two motorised valves or one ,please. The boiler recently started to fire occasionally when the timer was off and the pump runs even though the timer is off. The programmer was recently replaced so I don't think it's that. The programmer indicates that everything is off but the boiler power light still stays on. Problem: The boiler keeps running even though the thermostat is not calling for heat (the receiver in the boiler room lights up when the thermostat is calling for heat). The control system generally comprises several components, a programmer, a thermostat, a motorized valve and finally the boiler and pump. 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