Myson cylinder thermostat goosed?

[CBW]

Update: changed the 2 heads over, made no difference. Changed the cylinder stat for a new Honeywell. Need to check the temp. Boiler still fires up, then off, then about 2 mins later fires up again, and possibly another cycle after that (not sure if this has any bearing on situation).

Edited: I’m thinking the cycling maybe to do with the gas valve, as it makes a loud clunk when boiler fires and when finished. Is there a way to test this, or just replace?

 

[ianmcd]

• Earth to common 250 vac

• Earth to terminal 2 on demand 250 vac

• Earth to terminal 3 on demand 3.65 vac

Hi Chris where are you measuring these voltages ? the Myson (MPE222) doesnt have an earth, the brown and blue wires power the motor to open so should have 230V AC when there is a demand and 0V when no demand, the grey and orange wires are the microswitch wires that signal the boiler to come on, with no demand there should be no continuity across the grey and orange wires

 

[CBW]

Hi Chris where are you measuring these voltages ? the Myson (MPE222) doesnt have an earth, the brown and blue wires power the motor to open so should have 230V AC when there is a demand and 0V when no demand, the grey and orange wires are the microswitch wires that signal the boiler to come on, with no demand there should be no continuity across the grey and orange wires

Hi Ian, these voltages were across the Myson MCT1 (cylinder stat). I didn’t do any testing at the zv, as I just swapped the heads (from dhw to heating and vice versa) and changed the call wires over.

 

[MeldrewsMate]

@MeldrewsMate ...Also, if ch water was leaking into cylinder, wouldn't the water be discoloured?

Yes it would, but my suggestion was HEAT could be bleeding into the cylinder, not water.

 

[CBW]

Yes it would, but my suggestion was HEAT could be bleeding into the cylinder, not water.

Thank you for the response, I’m not really sure how that would happen. If what I’ve done doesn’t fix it, I might just pay someone who knows what their doing.

 

[ianmcd]

Mike ,have you checked for voltage at the S/L on the Suprima when no demand from the programmer ?

 

[CBW]

Mike ,have you checked for voltage at the S/L on the Suprima when no demand from the programmer ?

No I haven’t. So no demands at all, and check the s/l? Should be 0vac?

 

[ianmcd]

No I haven’t. So no demands at all, and check the s/l? Should be 0vac?

Yes no demand shouldnt have any voltage at SW/L