Problem- Worcester Bosch Greenstar 40 HE combi with Grohe mixer

[Rob_B]

I have no problems with one of the showers or the 4 sink basins in my house but when we use the main shower, the Worcester Bosch Greenstar 40 HE boiler overheats, giving error E9. This has started recently after 10 years of good working order.

Other facts:
1) The water temperature in the shower is fine.....until the boiler passes the temperature limit and cuts out. (When you turn the shower on, the boiler doesn't start to moderate the burner at around 70 C on the LED but keeps going up to 75+ and then passes the safety limit, cue error E9).
2) The problem seems to be resolved by reducing the water pressure going into the boiler i.e., half-closing the mains tap.
3) The nice plumber originally managed to kink the pipes leading to the other Grohe shower - so the pressure going into that mixer is lower. Not sure if this explains why this one works fine though.
4) We have high water pressure in our area - but that hasn't been a problem before.
5) The boiler has also given an EA error (no flame detected) when the CH has come on in the morning several times in the last few weeks.
6) The boiler was serviced and the electrodes replaced about 2 weeks before the problem appeared.
7) I tried running the shower without the head or hose - still gives the same problem

Does anybody have a clue what is going on? It is difficult to fully disentangle potential boiler from shower problems.

Thanks for any suggestions.

 

[Stanios]

The reason why your other outlets arent locking the boiler out is because you probably arent running them for 10-15mins at a time. This to me looks like a dhw thermistor fault, get a breakdown engineer or worcester to have a look. Bear in mind 10 years is pretty good for a combi boiler it might be better just to replace it whilst you are ahead.

 

[Rob_B]

Thanks for the reply, but that isn't really the problem. The boiler overheats within 30s of the "problem shower" being on, while doesn't cut out when the other shower is being used for 20 minutes +. It was serviced by a Worcester accredited engineer a few weeks ago and he said it was in good working order (after changing the electrodes).