Biasi M96 Riva Compact HE

[downthesouth]

Biasi ummmm.......
Right, I was called to a problem with this boiler last night, complaints of poor hot water temperature. Checked diverter valve, flow-rate, pressure all ok.
Boiler did not modulate up on HW. Checked Modulator coil 80ohms checked on/off coils top and bottom they seemed ok as well. So im going on the basis of either a stuck modulator coil or the potentiometer/rheostat isn't sending the correct voltages to the modulator. If the latter is the case then its PCB, Does anyone know the expected voltages on the coil for DHW? MI's say nothing, Biasi not that helpful. Also would the thermistor be suspect? the fan changes speed but not flame, but I thought the thermistor going out of resistance range shows up as fault on Boiler panel?!? Also more alarmingly when I checked gas pressures on P1 in Dhw mode it said 3mb!!!!! Checked for Leak, Governor on meter, pipework size all ok, Hob and fire connected on carcass ok as well, So whats up with the 3mb on P1!!!! Dont shoot me down in flames if I have missed the obvious, I am fairly new to the game, been doing it for just a year.
Any help greatly appreciated.

 

[northcarr]

Just a thought could be crap in the gas valve

 

[solutions]

Do you have a linear potentiometer to hand? You can pick them up at Maplins. Use in place of thermistor to alter resistance. If valve modulates then good chance thermistor is duff. Are there any dip switches on the board? I dont know the boiler well. Is it possible it can be range rated? What is the gas valve like on Central heating? Does it modulate? P1 on heating? Sorry only asking more questions but if it is modulating fine for ch then im inclined to think dhw thermistor is likely at fault. What ohms is it at room temp?

 

[downthesouth]

No i dont have one, thats a good call I will purchase one tomorrow. Gas valve P1 on heating the same. Modulation seems same on CH as well no real change, house was cold on start no change when I winded up CH stat on boiler, Im guessing modulation coil or voltage to it? potentiometer can check that as well I guess. Didnt get t check thermistor as it didn't come up in self diagnostics as a fault and I assumed (bum out of you and me, and all that) that if resistance went out of range, fault showed up! Will check thermistor as well, got a few spare somewhere.

 

[Ermintrude]

Be checking inlet of gas valve? Water in line?

 

[northcarr]

Do you have a linear potentiometer to hand? You can pick them up at Maplins. Use in place of thermistor to alter resistance. If valve modulates then good chance thermistor is duff. Are there any dip switches on the board? I dont know the boiler well. Is it possible it can be range rated? What is the gas valve like on Central heating? Does it modulate? P1 on heating? Sorry only asking more questions but if it is modulating fine for ch then im inclined to think dhw thermistor is likely at fault. What ohms is it at room temp?

Wouldn't it be just as easy to check the thermistor in place just use a multi metre on resistance or just change it if any real doubt they are only a couple of pounds.