Keston C36 combi boiler problem

24 Feb 2010
Reaction score
United Kingdom
I have a 3 year old Keston C36 combi boiler. For some time now, on occasion running the hot water tap or a shower etc causes the radiators to heat up. Yesterday, the boiler stopped giving hot water. All that happens is that the radiators fully heat up. The water temp on the boiler shows as 12 degrees, sometimes 10. However it does have the DHW light on when hot tap is on. The boiler also appears to overheat in this situation as can show at 80 degrees (when the heating is only set to 75 degrees).

Can anyone please suggest a possible cause?

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Its an issue with the divertor valve, get a Gas Safe engineer out to replace a small capacitor (part No. c10c420000) located on the wiring loom bottom right of the main heat exchanger.

There is no point in the engineer attending without that part so make sure he orders it before attending

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