Worcester 28i Combi Boiler hot water and heating needs resetting all the time

[Richard560]

Hi everyone,

Has anyone had an issue with this boiler tripping out (one second on/off fault flash) with both the CH and DHW (it's not the 28i greenstar version)


Central heating cuts out, running time gets shorter the higher the temp demand, will trip nearly ever time heating is on but then sometimes works for hours, best outcome set to minimum temp.

Hot water cuts out if any tap is on full, gets better if the tap is on slower, I could run the shower for 3 hours and it not trip out but this was in summer when we filled the pool up from the shower head via hose pipe, showers are usually ok.

It's had the following
1. Flame sensor in may (no change) I did let them know the next day but no reply until I complained in September lo leasing agent when we needed the heating again.
2. New control board end of October (no change)
3. New thermostat (guessing he mean the overheat stat, still no change, even worse now)
He's checked the thermistors for the CH and DHW temp and says their in the correct operating range.

Now I noticed when the CH system is cold the pump will run on all 3 speeds without any issues, I can listen to it via a screwdriver and sounds fine on all 3 speeds.
once the system is hot though, on speed 1 there's no pumping at all (listened to pump with the screwdriver again and you can hear the mains hum from the coil) change to speed 2 and You can hear the propeller start up but sounds very slow and it sounds like its catching on the insides, speed 3 seems good with a good rush of water.

boiler trips out quicker on speed two and you can hear the water getting very hot in the boiler so pointing to overheating, same happens if CH temp is set to max and you can hear the boiler kick into max burn mode as the two speed fan speeds up and then drops if you reduce the heating temp dial.

With the hot water I noticed running the tap at the same flow rate as the shower it would nearly behave its self (until they changed the overheat stat on Friday),
running the tap faster you can hear the boiler going to max burn mode as the fan speed changes and you can hear the water getting really hot then it trips out.

Now here's the odd bit that no one can find info on inc Bosch tech support according to boiler guy, when the system is running the burn ok light goes out (doesn't sound
Ike it's getting really hot), then you hear/see it sparking through the viewing hole as if it's lost gas, but the flame looks just the same as when it was running, it stays there for about 4-5 seconds while still sparking and then slowly fades away, spark stops and the reset button starts to flash (hence the new flame sensor and then control board being fitted)

I did notice the flame isn't all blue like it should be as there is random orange flames popping up all over the viewing hole area.

I'm wondering if the heat exchange is all crudded up, pumps not the issue for the hot water problem as it's not used during that cycle, runs afterwards for a couple of seconds like it should do.

Going to test the water temp coming out the boiler tomorrow to see if it rises before tripping out.


Has anyone else come across this issue before and if so what was it in the end?

Cheers
Richard

 

[Richard560]

progress today

I found that the flame sensor wire was tight and that was possible causing it to short on the bottom of the burner housing when it got hot as since I've put a little slack into the wire the boiler is fine or checking all the connections solved the issue, oddly this fault started after a service (which pulls on this wire when the controller is removed and left hanging to gain access to parts) also found a fuse roaming around loose in the controller casing right where the connection is for all the sensors so could of been touching the circuit board

So far so good, interesting how the manual doesn't show the pressure switch in the circuit block diagram but it does come under the same fault table chart test D and is wired in series with the overheat switch.