British Gas 330+ boiler appears to be randomly heating the hot water

4 Oct 2021
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United Kingdom
Hi, I have a nine year old 330+ that up until now functioned perfectly. But over the last two weeks I have noticed a weird issue that the system appears to be choosing random non programmed times to heat the hot water. Not every day, just some days.

I use a Tempus Seven Control panel which is over 20 years old. I also have a separate hot water tank but I have no idea whether that could also be heated by electricity.

I had the hot water turned off completely on the panel yesterday but the hot water started at about 11pm all the same. The only way I could get it to stop was by powering off the control panel via the switch by the hot water tank. Which I guess does point to the controller being the culprit.

The boiler has an "at rest" - i.e. not heating anything - temperature of 34 C. Does that sound correct? The boiler has been professionally serviced every year by a local plumber so I will be calling him in. But I would like to have an idea of what the problem could be first.

Photo of hot water boiler, showing the switch I pressed to power off the panel. Presumably it also powers the pump?

Any assistance would be much appreciated. Thanks
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