Hot-cold-hot-cold, even when pressure restored,Worcester 240

4 Apr 2007
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United Kingdom
Worcester Bosch 240 Combi RSF

The boiler was making groaning noises, the 'hot' water was running cold then hot then cold. Looked at pressure gauge and it was about 0. Restored pressure as per post on here, got it back to the just-more-than-1 indicated by a red marker on the dial.

No more noises, but the water still runs in cycles of hot and cold for a minute or so each (both upstairs and down, CH on or off).

Just before you feel the hot water run cold, there is the sound of ignition in the boiler and the flames can be seen through the little window.

Can I do anything or do I need an engineer? Is it likely to be expensive?

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Possibly calorifier scaled up or hot water sensor capute.
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