ravenheat csi 85A: hot + cold DHW, now red light and no ignition

[AS2015]

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.

 

[TCCHeating]

Overheat thermostat has tripped. There is a manual reset behind a round screw out cover on the fascia. You need to call an engineer. The symptoms you are suggesting are a common fault on combis and it won't take long for a good engineer to diagnose the problem. In fact most will know what the problem is before even seeing the boiler

 

[AS2015]

Thank you for your reply.

When i got home i decided to have a look at the boiler before i called an engineer. It was still refusing to ignite, instead repeatedly going to the red light described above. I switched it all off and removed the main cover and then internal cover. When i tried the start-up again i could see that the fan was working (i knew it wouldn't ignite without achieving compression first but wanted to check fan started ok). I switched it all off again and then made sure the tubes to the air pressure switch were free and secure (not sure how to check the air pressure switch works as tube too short to reach to blow / suck as suggested on some sites). I removed the spark ht leads and checked the connections, removed and checked the spark plugs, used a vacuum cleaner on the burners and then reassembled.

When i turned it all on it fired up straight away but the spark continued for several seconds while the flames were lit and then the flames went out, it repeated this a couple of times then it stayed alight for the rest of the evening. This morning it fired up first time and the hot water was much more consistent with much longer hot phases and shorter cold phases in the remaining hot / cold cycle when running hot water. There was no sign of the red light after my shower and the heating had been on for one hour this morning.

I am still concerned about the hot - cold repeating cycle on the hot water. I'm not sure what i achieved last night but it went some way to improving the hot water consistency, so there is obviously something still not quite right and i'm hoping someone can point me in the right direction (i appreciate one member has already said to call an engineer, which i still may do but it is 1 week before christmas and for the £80 call-out charge i was quoted i can buy and fit many of the usual thermostats and spare parts myself unless it is part of the gas system).

Again, any further advice would be appreciated.

 

[Agile]

The further advice is that you should not have opened the combustion chamber as a DIYer. It provides the room sealed safety of the boiler.

The correct procedure now is to call a gas reg engineer to check it and repair it.

Tony