central heating fault?? Can keep warm but costing a fortune!

[UKL200]

Hi, just looking for some advice..
I have a
potterton prima f boiler,
potterton EP2002 controller,
PRT100 mechanical thermostat,
MYSON power extra valve,
europa circulating pump

the trouble i'm having is when i turn my heating on on the controller, the light comes on but the boiler doesn't try to fire. the h/w side works perfectly though..

The power extra valve lights correspond with the lights on the controller so if i put the water and heating on together the house gets warm.

I could really do with turning the water off though as i'm on a meter and it's using gas before i can buy more lol and with a newborn around in this weather i'm having to just bite the bullet and leave it all running..

Does this sound like a thermostat problem? It does click still when i turn the dial..

Any help much appreciated, i'm technically minded but never needed to fix central heating apart from a sticky fan..

regards UK_L200

 

[Boilerman2]

The system has probably not been wired to allow Heating ON Hot Water OFF, for Heating only operation to occur the Hot Water OFF Terminal must be wired from the Programmer to the N.O. terminal of the Cylinder stat, in order to force the mid pos valve to the Heating only position

 

[D_Hailsham]

Are you saying that you can only get heat when the hot water is being heated?

If so the fault is in one of the following:

Programmer
Cylinder thermostat
Myson valve

Quick check

Turn CH and HW ON at programmer and turn CH and HW stats up so boiler is alight.

Turn HW OFF at programmer.
Does the boiler stop?

Turn HW ON at programmer
Turn HW stat to MIN
Does the boiler stop?

If boiler STOPS in both cases, the Myson valve is faulty. But if the boiler stays on on one case but not the other, the fault is in the item which has been turned OFF (programmer or stat).

If you have a multimeter, you can also check the voltage on the valve's grey wire. It should be 0Vac (measured to blue wire) when CH and HW are both on and 240Vac when HW or the stat is turned off.

If it's 240Vac in both cases, the valve is faulty. If It's not 240Vac in one case, then that tells you the tested component is faulty.

 

[UKL200]

ah good stuff thanks.

Exactlt, only heating radiators with both switch on (though they did work independantly before).

The first test went as you described,

when i switched the stat down to 20 on the cylinder the c/h system worked as it should, regardless of h/w settings.

Oddly i've turned the stat back to 60, and it's still working as normal now.. Temp fix ta

i've noticed on the bottom of the myson valve there's a switch/adjuster? It feels a bit flimsy whatever it is.

Cheers again for your sugestions

 

[D_Hailsham]

The first test went as you described

So the programmer is OK and so is the valve

when i switched the stat down to 20 on the cylinder the c/h system worked as it should, regardless of h/w settings.

So you turned the HW on and off while the stat was on 20? I don't remember asking you to do that!!

Oddly i've turned the stat back to 60, and it's still working as normal now

It sounds as if the valve may have been sticking in mid-position

i've noticed on the bottom of the myson valve there's a switch/adjuster? It feels a bit flimsy whatever it is.

Do you mean the metal lever that can slide in a slot? It's there so the valve can be opened to mid position (locked in the MAN position)when the system is filled. When the system is off, the lever should be at the Auto end and there should be resistance when the lever is moved to the Man end. When CH + HW or CH only is required, the lever should be floppy in the slot.