Heating only working when hot water is on

[gixer1979]

I live in a 4 yr old Barratt house with a Potterton Promax HE Plus setup.

My central heating has developed a fault over the last day or so where by the radiators will only warm up when the boiler is warming hot water in the tank.

When just the CH is in the on position the boiler doesn't even offer to fire up.

I have a standard mechanical thermostat which although i have stripped down and checked with a voltmeter seems to be clicking as it should do when the temperature is adjusted. Visually the Electronic programmer also appears to be fine.

Any advice on where i should start ??

 

[Agile]

Faulty motor valve?

Tony

 

[gixer1979]

Motor valve was my old mans initial thought when i rang him. Inside the cupboard at the top of the stairs i can see two holywell motor valves. One mid way along the pipe that feeds the water tank (im assuming this one is the HW one) and another which is plumbed in just where a pipe comes from downstairs. Im guessing this one is the CH valve.

If the valve was faulty would switching it to the manual position be likely to make the CH fire up ?

Im a bit of a central heating novice if u hadn't already guessed.

 

[seco services]

If the valve was faulty would switching it to the manual position be likely to make the CH fire up ?

no.

it sounds like its opening by the motor but not activating the m/switch.
when the heating stat is turned up is the lever on the end of the valve loose with no resistance ?

 

[gixer1979]

Yes when the thermostat is turned up high the lever on the end of the valve is loose. if i turn the stat down to a temperature lower than the current room temp u can instantly hear the valve move and the lever has resistance again.

 

[seco services]

ok so the wall stat is opening the valve but not activating the micro switch inside to give power to the orange wire.

you can test this with a multi meter.

 

[gixer1979]

Where would i find the orange wire. The valve just has a black cable coming out of it which disappears under a false floor in the airing cupboard. Is it that wire i need to trace ??

 

[seco services]

all the wires useally meet up in a wiring centre like this.

the black cable will have 5 wires.
brown is live from stat
orange is sw/live to pump/boiler

 

[gixer1979]

Found it removed the top and i can see the orange wire now, need to find the voltmeter from the garage now and i'll test it.

If i have no voltage on that wire when the stat is turned up is it a replacement valve needed ?

 

[seco services]

make sure you have no call from the hw as the orange from the hw valve go's into the same connection.

what valve make/model is it ?
replace actuator if its a faulty m/switch.
maybe be a sticky valve stindle.

 

[gixer1979]

As suspected the orange cable is dead, no voltage at all. It must be something sticking because it sprang into life this afternoon for a couple of hours.

Its a honeywell valve so i assume replacement is the option.

 

[seco services]

i would take the top off and check.
if it sprung into life its poss a sticky valve spindle by crud in the system.
with heating off push lever across afew times it can free the spindle up
depending how sticky it is.

 

[gixer1979]

Doesn't seem to have done anything. To be honest i dont use the hot water one as i always heat the water with the immersion timer.

What do you reckon to swopping the power heads over to prove thats the fault ?

If that did the trick im assuming i could replace the power head on the hot water one at my leisure.

 

[seco services]

Doesn't seem to have done anything. To be honest i dont use the hot water one as i always heat the water with the immersion timer.

thats a dear way to heat it.

What do you reckon to swopping the power heads over to prove thats the fault ?

you can
or remove the heating one and you can operate the spindle better to see if it'll run smoother.

If that did the trick im assuming i could replace the power head on the hot water one at my leisure.

you can but personally its cheaper to heat by the boiler.