Ultracom has problems when asked to supply higher output?

[Rog200455]

This problem has crept up on me. Glow Worm Ultracom 30CXi installed in 2007. I normally run the boiler ranged down to 12kW for heating and there have been no problems. Recently, when taking a shower, the hot water goes cold, maybe hot again once but then the boiler seems to go into "limp mode", working but at low output, as shown by 1 "flame" in the display.

So, I ranged the boiler back to 24kW and checked the heating by turning the stat up. Initially, the display shows 5 "flames" to indicate maximum output, but then drops back to the limp mode, as above.

At first I thought the problem was a blocked plate heat exchanger but it's not that, as the same fault occurs whilst in heating mode as well as DHW.

As I write this, the boiler is heating fine, ranged back down to 12kW.

Any ideas please?

 

[ianmcd]

When you range rate the boiler that only has an effect on the Heating side it has no effect on the HW side, does it only happen with the shower ? are the other HW taps fine ?

 

[Rog200455]

Yes, the hot water side always has full power available. If I run the bath tap, then the same fault occurs. As I mentioned, the fault is also with heating but only when I set the boiler back to 24kW.