Central heating switching off occasionally

[darren61]

I'm having a problem with my central heating, I presume it's a gravity fed system as there is a cold water tank in the attic, a cylinder in a cupboard and a boiler in the garage.

the problem is if I turn the thermostat on the hot water cylinder down the heating goes off

leave it on full and it works OK but you have to be careful when running hot water

Any ideas

Thanks

 

[ChrisR]

Need more details - is the pump running when the heating is on/off?
Any motorised valves about the place?
What boiler?
WHat timer/programmer?
Got a room thermostat?

 

[gasman1234567892001]

its wired up wrong at the clock

 

[wilhelm]

do you mean a complete "clock up" ?

 

[felix]

I suspect you have one of those simple systems in which the HW runs on gravity alone but the CH is pumped. In such a system the boiler has to go off when the water in the cylinder is hot enough. This may be done either with the boiler's own thermostat or, as in your case, with a tank stat. To get CH you start the pump.

The drawback with such a primitive arrangement is obvious; no HW demand = no boiler. To get CH on its own you need a way of blocking the gravity driven flow of boiler water through the cylinder heating coil. This has to be a motorized valve of some sort. Have a look around your system and see what you've got. In particular, trace out the pipework from boiler to cylinder coil and back.

While you're at it, take note of where your feed and vent pipes join the system.

 

[wilhelm]

if its that primative, twill not have a cyl stat.

 

[wilhelm]

although, i have seen primative set ups with a cyl stat,
with motorised valve, powered separately


blimey what i mean is a very early c plan arrangement..

but not c plan..

 

[felix]

Unfortunately, I have seen a gravity HW / pumped CH system with a tank stat. It was in a house we bought. There was a motorized valve too but the tank stat only controlled the valve, not the boiler. The boiler, which was in an outhouse, was left bubbling away to itself once the cylinfer water was hot enough. I know which plumber did it because the previous owner left us all the bills.

I'd already looked in the loft and fished a piece of rotting hardboard with a hole crudely smashed in it out of the cold water tank. This tallied with a bill from the same plumber for "Fitting lid to cold tank". Needless to say, he got no more work at our address! I'm not trying to say that all plumbers are cowboys but there are plenty around. But I digress ---

There are some good plumbers on this forum. Find out as much as you can about your system. The truth is in there.

 

[croydoncorgi]

Possibly you have a faulty zone valve on the CH which IS opening but is not operating its internal switc, so when the room stat calls for heat, the valve opens but nothing else happens. With the hot water being heated, the boiler and pump will already be running, which is why the CH works at all.

Easy to check if you're competent with electrics. Otherwise Get Someone In.

 

[darren61]

Need more details - is the pump running when the heating is on/off?
Any motorised valves about the place?
What boiler?
WHat timer/programmer?
Got a room thermostat?

The pump doesn't run when unless you turn the boiler thermostat up then the pump runs and the heating comes back on.

there is a motorised valve in the airing cupboard with a lever on it, i'm told this lever should have tension but it just moved back and forward with no tension.

The boiler is a Myson economist


Timer is a Randall 102

Room thermostat in the hall

Sounds like it may be a problem with the motorised valve, is it a simple job to change it or do I need to get a plumber in ( plumbers are excused from answering the last question)

 

[darren61]

 

[MANDATE]

The actuator head can be removed from most motorised valves and with it off you can check the valve spindle for stiffness. You can also watch the actuator move and confirm it moves to the correct positons (proving the motor) Also in the 'central heating' position the 'orange wire' should become live so you can check this at the terminal box. (if not live likely cause is failed micro switch. A replacement head is around
£36 and fitting about 20 mins. ( well mine was )

 

[tech]

don't Diy :

Get the system checked by a corgi engineer you could save yourself £,s in the long term .

*The pump turns on when i turn on the boiler stat*

 

[weargas]

don't Diy

but this is a diy forum

so vindictive,
so pedantic.

 

[tech]

so true *