Combi boiler problem

[chrutch]

i've got a gloworm compact 80e combi thats giving me trouble. when the heating goes on its only luke warm - the gas burner only fires at a low level! when i turn on the hot water the same thing happens - only luke warm hot water. in addition the boiler only fires up for hot water when i turn the kitchen tap on (high flow rate), but when i turn on the bathroom basin tap (lower flow rate) the boiler doesn't fire up at all?? not sure if this is part of the same problem or something separate. is this a diverter valve problem, or a temp sensor problem, or a flo rate sensor problem?
does anyone have any ideas??

 

[methaneman75]

Thermistors :- With the power off unplug the connector and test resistance is 10k ohms at 25°C
If you have a decent multimeter you could try this
Could be a few things causing possibly gas valve or modureg issue as well but you would need a dog card for that

 

[bellairaphon]

when hot water is on do the heating flow pipes heat up??? another for the luke warm water could be dhw thermistor

 

[chrutch]

Thermistors :- With the power off unplug the connector and test resistance is 10k ohms at 25°C
If you have a decent multimeter you could try this
Could be a few things causing possibly gas valve or modureg issue as well but you would need a dog card for that

Ta for feedback - will try measuring thermistors, but whats a dog card??

 

[chrutch]

when hot water is on do the heating flow pipes heat up??? another for the luke warm water could be dhw thermistor

No, the CHTG pipes do not heat up when DHW is on, which i believe discounts a DV problem. any ideas why i get no fire up when basin taps are on??

 

[kevplumb]

CORGI

 

[namsag]

Fault finding chart tells you to check for 2 different voltages at the gas valve ,one brings it on the other allows it to go to high flame quite common pcb does not give out correct voltage for gas valve to go to high flame.

Having to turn tap on full at certain taps suggests the diaphragm is also on its way out.