3 port keeping the heating on?

[doitmyself]

Gonna go fit a Drayton later an see what happens.

Before you do that, check the voltage across the gas valve when the fault occurs. If it's low, i.e not 230V, the GV is faulty.

 

[spikewt]

Not sure how that would help as the fault occurs before the gas valve initiates. Its all down to the boiler being activated by switch live having 89v staying there once the heating is satisfied.
Next time you work on a three port, have a look. Switch it on on, call for heating but not hot water, then turn the room stat down. The valve will keep the switch live at 89 or so volts. Common thing so I here.
Reason why it don't show up often is due to boilers having high voltage side and low voltage side. On Biasi boilers, the same terminal is used for high or low voltage so it seems like the boiler gets confused.

Definalty one to remember now.

 

[bigads28]

May have the answer now.

Biasi were really helpful. Turns out most 3 port valves have this problem. It's apparently the way they work.

Biasi said do one of 2 things. Either fit a Drayton as the residual voltage is below 60 so they say or fit a capasitor of 0.47 microfara across the switch live and neutral to take the voltage away.

Gonna go fit a Drayton later an see what happens.

Great hope that sorts the problem out. The heads pop on and off those Draytons really easy too for future repairs.

 

[happyflyer]

I hate guessing on here, if you had the motor winding in series that might give you that low voltage, you need to check
that wiring 80VAC is an unusual voltage in anyone's book, start again with the wiring

 

[spikewt]

SOLVED!

the Drayton valve had a residual voltage of 12v so didn't activate the switch live once the heating was satisfied.

Love it when a problem like this is solved finally.

My sparky spoke to a big plumbing firm he works for and they came across this too. On Worcester boilers!

 

[Aquazone]

You can get a resistor/relay whatever you call it from Worcester (I think I have posted part no before) that goes between SL and N to counteract this, as I have has Worcester PCB's chattering due to this stray voltage

 

[solutions]

You can get a resistor/relay whatever you call it from Worcester (I think I have posted part no before) that goes between SL and N to counteract this, as I have has Worcester PCB's chattering due to this stray voltage

I have used a capacitor in the past to soak away the stray voltage. First time I came acriss it was when one was supplied wuth a new pcb for a glow worm micron which explained that its job was to deal with stray voltage from 3 ports. Not needed on s plan.