I have a ravenheat csi 85A condensing combi boiler. Recently the hot water started running hot for a few minutes then started running cold then hot then cold repeatedly in 10-30 second phases. There is less of a change in temperature if the central heating is on as i guess it is stealing heat from that while waiting for the boiler to heat up again. When i looked at the boiler with the hot tap on it all runs fine then the gas burners go out, which makes the water cold, then the boiler restarts after a few second to heat the water again. This occurs even with the thermostat turned to maximum for the hot water and central heating. A couple of times this problem has continued until the red flame / overheat failure light comes on. Two weeks ago I drained then cleaned the whole system with sentinel x400, then drained and refilled with sentinel x100 inhibitor which fixed the problem for a week then it came back again.
This morning the boiler lit for 5 minutes (but only when running the hot tap and central heating at the same time) but then went to a red light. It now will not light at all for hot water or central heating. Instead it goes straight to showing the red light. The pump turns on, the fan doesn't start, there is no ignition clicking nor ignition at the burners and after 30 seconds the red light shows. Any useful advice would be appreciated.
This morning the boiler lit for 5 minutes (but only when running the hot tap and central heating at the same time) but then went to a red light. It now will not light at all for hot water or central heating. Instead it goes straight to showing the red light. The pump turns on, the fan doesn't start, there is no ignition clicking nor ignition at the burners and after 30 seconds the red light shows. Any useful advice would be appreciated.