It'll run the CH for 5 minutes, then turn off for 5 minutes, repeat. 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). I am wondering whether it is the Honeywell aquastat controller.I have model L4080b on the boiler. To get the pump to stop going I have to turn off the boiler at the mains. Boiler is about 5 years old as is the thermostat. This issue has been going on for sometime but gradually getting worse (pump runs for longer and longer). The pump may be getting a live feed from the programmer. The boiler recently started to fire occasionally when the timer was off and the pump runs even though the timer is off. The CH works fine, but sometimes, when it’s been on, the boiler continues to fire and the pump in the airing cupboard continues to run, after it should have gone off, ie the boiler programmer shows that the CH (and HW) is off, but the boiler and pump keep running. 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. Only resolution is to switch off at power socket. Hi , OK ,helps now have the model of your boiler. 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. 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. Vaillant boiler firing up when heating is off I've moved into a new flat that has a vaillant boiler. Even if I turn the thermostat off, the boiler keeps running. The programmer indicates that everything is off but the boiler power light still stays on. Even when you shut off the heat at the programmable thermostat the boiler keeps running. 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? :help:I have a two zone Smith GB100W gas boiler that still runs after the thermostat has reached the desired temp. The programmer was recently replaced so I don't think it's that. Turning the room stat made no difference and there was no clicking. I replaced the thermostat to no avail. Be very careful if your boiler is outside and you are turning it off at the fused spur. The only thing that will fire the boiler when it is off at the programmer is the frost stat. 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