Baxi 105e

[macman1]

I cannot get hot water, my CH works and I can get HW when its up to temp. If I turn tap on without CH on it flashes the pumo/low pressure fault. I have changed the top diaphram. any suggestions pls ?

 

[twgas]

Check the pressure, should be 1 bar(ish)
Does the HW demand light come on when you run a tap?

 

[macman1]

Pressure is just over 1 bar, HW demand light comes on then it won't ignite a few seconds later the fault on pump light flashes. the pump is running but does get hot quickly.

 

[twgas]

If the pump gets hot without the boiler running i would have to say its not working (motor turning, but not the impellor). Or no water in it.

 

[macman1]

the pump is working because when I put CH heating on house heats up as normal, Can get HW when heating is on but don't want heating on this weather, I open tap, demand light comes on, pump starts but then doesn't go to the next step and ignite the boiler.

 

[twgas]

I would be suspecting a blockage in the plate h/ex, preventing circulation.

 

[mfarrow]

There's two microswitches actuated by a pin each from the diverter valve unit, one at the top and one at the front. One comes up with the tap open to confirm the demand for HW.

The other pin comes up when there is sufficient flow from the pump to actuate the burner, confirming the pump is functioning.

Does the second pin rise up and actuate its microswitch when the pump comes on on HW setting? If so then suspect PCB or switch fault. If not then suspect pump or diverter valve.

If no to the above, and the second pin rises OK on CH then as suggested it's most likely the plate heat exchanger faulty, especially if your water goes hot/cold or is only luke-warm. The residual pressure from the CH actuation is likely keeping the pin up when using the HW, even though the flow is too low to lift the pin on a cold start.

You can see the two switches pins in the picture below. One at the front is a bit blurred but one on top should be clear.

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