Boiler overheating after isolating F/R?

[Stu666]

Main Combi Eco 30 boiler. I have some work planned changing radiators and pipework, so decided to drain the central heating system down. Could take me some time to finish the work and we need hot water in the meantime, so I decided to move the selector to hot water only and isolate flow and return via the levers beneath the boiler, then repressurised the boiler to about 1.3 bar via the filling loop (remembering to close this afterwards). All seemed well, ran hot water, got warm for about 10 seconds, then went cold. Boiler flashing E110 overheat warning and pressure had risen to 2 bar. Making a noise like a fan or pump is running. Tried switching off and on but I suspect it's still too hot as still flashing E110 and noisy. Any ideas? Wondering if I've possibly isolated the wrong levers? Have circled in red the ones I moved.

 

[Johntheo5]

Have you shut the right valve(s)??

 

[Stu666]

Have you shut the right valve(s)??

View attachment 389863

Thanks. Yes, according to that diagram, I've closed 12 - Heating Return and 16 - Heating Flow.

 

[Stu666]

I've capped off the pipes for now, opened the F/R levers and refilled the system. Seems to be working OK after a reset. Strange that it doesn't seem to like me isolating flow and return?

 

[CountryFan]

Wonder if diverter is stuck

 

[Johntheo5]

Main Combi Eco 30 boiler. I have some work planned changing radiators and pipework, so decided to drain the central heating system down. Could take me some time to finish the work and we need hot water in the meantime, so I decided to move the selector to hot water only and isolate flow and return via the levers beneath the boiler, then repressurised the boiler to about 1.3 bar via the filling loop (remembering to close this afterwards). All seemed well, ran hot water, got warm for about 10 seconds, then went cold. Boiler flashing E110 overheat warning and pressure had risen to 2 bar. Making a noise like a fan or pump is running. Tried switching off and on but I suspect it's still too hot as still flashing E110 and noisy. Any ideas? Wondering if I've possibly isolated the wrong levers? Have circled in red the ones I moved.

 

[Stu666]

Flow pipe, comes down the rear of the boiler and then a couple of 90 degree bends up into it. It drops down to a 15mm run below, which feeds a nearby rad, this is a later addition.

 

[Stu666]

Wonder if diverter is stuck

Haven't had any issues with either CH or HW. Unless it's a new problem that's occurred recently. Don't think the heating has been on in a couple of months. Guess I'll find out once I've finished putting in new rads and pipework

 

[Johntheo5]

Where did you cap the flow&return pipes?

Have you tried shutting the isolating valve on either the flow or the return to see if you get HW with one of them shut off?. Its strange because the diverter valve must have changed over, otherwise no primary HW will flow throuh the PHEX.

 

[Stu666]

Where did you cap the flow&return pipes?

Have you tried shutting the isolating valve on either the flow or the return to see if you get HW with one of them shut off?. Its strange because the diverter valve must have changed over, otherwise no primary HW will flow throuh the PHEX.

Currently just capped at the valves where I've removed a couple of rads.

Just tried shutting the isolating valves, first flow, then return, got HW both times. Then tried with both valves shut, worked fine.

Wondering if it makes any difference closing the isolating valves before draining the system down? When I drained it earlier, I closed the valves once all pressure had gone, then repressurised the boiler once I realised we needed HW.

 

[Johntheo5]

Possibly air in the system after depressurizing/refilling, most of these automatic air vents (AAVs), item 27 above, are inaccessible (legally), and more often than not, are shut off after boiler installation to avoid then dribbling water if left open.

 

[Stu666]

Possibly air in the system after depressurizing/refilling, most of these automatic air vents (AAVs), item 27 above, are inaccessible (legally), and more often than not, are shut off after boiler installation to avoid then dribbling water if left open.

That would make sense given it happened immediately after depressurising/refilling, and some of the noises it was making (kettling?). Is it likely to resolve itself when I drop the system again and bleed the rads once refilled? Or is it a job for a pro?

 

[Johntheo5]

Once rads bled after refilling, suggest starting up the boiler on CH for 10 minutes or so then open a hot tap at a fairly low flowrate initially at a fairlly low DHW temperature SP, then back to normal.