F.83 error specifically when boiler turns on by itself

30 Nov 2023
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United Kingdom

We have a Vaillant ecoTEC boiler 424 (open vented).

When we turn on the heating or hot water, it works perfectly. It can run for hours with no problem.

However, every now and then (seems to happen at least one per day) the boiler tries to turn on by itself (anti-seize maybe?). When it does this, it shuts off and gives an F.83 error.

Often this happens during the night, so when we come down in the morning the F.83 error is showing.

Can anyone help explain why this is happening and how we might be able to fix it?

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If the boiler is actually coming on then more than likely you have a sticking microswitch in one of your zone valves
Thanks! Would you be able to explain a little more? Why would this be the cause of the f83 fault, for example? Thank you!
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For anyone else having this issue, it appears that our pump was not correctly wired to the boiler. As such, when the boiler turned on by itself, it was unable to turn on the pump, leading to no flowing water and an overheat. However, when turned on my the honeywell controller, this did enable both the pump and boiler to turn on, which is why it worked fine to run the boiler during the day when we requested heating.

To solve the issue, apparently we need to change the wiring between the boiler and pump.

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