Mid position Valve

stem · 6 Dec 2013

scooby0606 said:
Got up and observed no hot water so:

Progammer shows heating constant (but up to temperature on stat)
Water constant. Felt pipes around MPV, hot to heating, cool to water cylinder

Voltage at MPV white 0 grey 250

That may be an indicator of your problem. The the grey wire is only made live when hot water is not required.

The hot water not required signal comes from either the hot water 'off' connection at the programmer, or the changeover contact on the hot water cylinder thermostat which is energised when it switches over from 'call' to 'satisfied'

Looking at the test you describe above where you got up and there was no hot water, assuming it was selected 'on' at the programmer and the hot water cylinder thermostat was calling for heat, the grey wire should not be 'live'

scooby0606 said:
Thanks again.

I observed the water didnt seem to be heating again so re-metered it:

White 0 Grey 250

There it is again, the 250V hot water not required signal present when actually hot water is required.

scooby0606 · 6 Dec 2013

thanks for your reply.

THis in mind where is the fault likely to lie? Its worked fine for 3 years and at first I thought MPV head, but now Im wondering programmer. Light on to indicate water / heating constant, but not sending signal ?

Ive discounted cylinder stat as the fault occurs with heating sometimes as well and obviousley thats not used then !

THis also key:

Turned off heating on programmer (from const to off)

Heard MPV move, boiler fired pump started and pipe to cylinder started to warm

Why when I turn off the heating at the programmer (from const to off)does the water automatically decide to fire up

scooby0606 · 6 Dec 2013

Read somewhere the programmer I have (ST9400c) can be a bit iffy.

Thoughts on jumping in and replacing this ?

scooby0606 · 7 Dec 2013

Been listening to the programmer this morning, it certainly seems that if both const lights are showing and you turn off the heating you hear one relay click (heating off) and the other click and water fires up. Tried heating on water off, switch water to const and although the light comes on there is no relay click and no valve / boiler activity

D_Hailsham · 7 Dec 2013

D_Hailsham said:
Mid-position valve operation and fault finding should help you sort it out.

The fault finding info in the above link will save you a lot of guesswork, particularly as you have a meter.

scooby0606 · 7 Dec 2013

going to run through them again, I already know they have read incorrectly in the past.

I just remembered I used to know a plumber so called him and he reckons valve 100%. Said as water and heating working independantly programmer will be ok, was very sure it was circuit board / switches in mpv. I told him I metered it but kept going on about back currents !

scooby0606 · 7 Dec 2013

Ok, completed all the actuator tests in the guide and it passed them all.

Does this cover off the problem I have:

Heating on- water does not come on when required

or

Water on - rads do not come on when required

ie both 'channel' operating at the same time ? not just switching from one to the other

Thanks

scooby0606 · 7 Dec 2013

Ok, went to screwfix and got a new programmer. Slotted it on the existing back plate, set heating on water off...... all good. selected const for water.. 'click' went the programmer (relay) and the MPV moved and the water started heating

Problem solved, iffy programmer, old one couldnt run heating and water at the same time, the relay clearly didnt flip

TCCHeating · 7 Dec 2013

Dont throw your faulty programmer away! Check the label on the back. If the batch number is between 1037 and 1139, ring honeywell for a free replacement. Then stick it on ebay! Thats what i do! Those dodgy batches have earned me a small fortune

scooby0606 · 7 Dec 2013

TCCheating, thanks for the advice. I had checked this due to an earlier post I read, My code is 1008, just short

Tom1981 · 7 Dec 2013

Most of the time the PCB in the Powerhead has given up. Ifyourgetting the correct demands and satisfies in to the head, change it

scooby0606 · 8 Dec 2013

Thanks for the reply TOm, Replacing programmer had already fixed it (see above)

Thanks to all

scooby0606 · 16 Dec 2013

Well well, Got a free new unit from Honeywell today even though the faulty unit was over 3 years old (only 1 year warranty) and outside of the faulty batch range... Ebay here it comes !

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Mid position Valve

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