Central Heating cutting out after a few hours

[norbo]

Sorry if similar question has been asked elsewhere - I have searched and can't find anything matching my problem.

My central heating system has been working fine for years and years but recently the heating seems to stop after its been on for a couple of hours. The pump seems to stop (I presume - because I can no longer hear the whirring type sound I can normally hear if I listen closely to one of the radiators!!) and the radiators gradually cool down. This happens before the heating is due to go off - as programmed on the timer. Hot water seems totally fine.

I have a Glow-worm space saver boiler (old!) and a Sunvic Select timer/programmer (a few years old). Does anyone have any idea what could be causing this problem. Could it be a fault with the timer? or something else stopping the pump? Room thermostat perhaps?

I am not a plumber and have only a basic idea about how CH systems work and have no intention of trying to fix this myself, but would really appreciate any help from anyone in the know.

British Gas have been out to look at it, but all they did was say they didn't know what the problem was and charged my £150 to change an air separator (I think) that they thought might be sludged up (this did seem to be slightly magnetic so he was probably right). This failed to solve the problem however, and the only other thing he could suggest was a power flush, but I'm not prepared to pay for that when I'm not convinced it will have any effect. The water coming out of the radiator bleed valves is totally clear.

Would really appreciate any help

Thanks

 

[big-all]

heeelllooo and wellcome norbo


no expert
but using the bleed screw wont proove much as the sludge is at the botton and not mixed with the water !!!!

 

[namsag]

First of all phone them back as they have not fixed the original fault and so you want what you actually paid your money for not what the guy mis diagnosed.

Do you have motorised valves on your system usually silver boxes just after the pump... It is not unusual for the motor in these to break down under use and turn it`s self off allowing rads to go cold. And when it cools down it will come back on an work for a few hours again before finally packing up.

 

[norbo]

Thanks for the replies! Yes, namsag, there is a Honeywell motorised valve as you describe - next to the pump in the airing cupboard where the hot water tank is. Is there any way I (a complete amateur remember) could check if what you describe is happening? This seems to match exactly the symptoms. Maybe I should just call BG back in again (maintenance contract) and get them to look at it for me.
Many thanks for your help

 

[namsag]

lever on silver box should offer no resistance if you push it over when there is a call for heat. If no call for heat it should have a slight resistance as the motor moves So if everything is calling for heat and there is no heat. Check the lever for resistance if there is some or it feels jammed up it is the motor

 

[norbo]

There doesn't appear to be any resistance when I push the lever.
As a matter of interest what does this lever do? Does it show the position of the valve or is it a switch or what? On the casing it says "auto" at one end and "manual" at the other end.

 

[gavinda]

if you're on contract..book your call then crank the heating up..when the eng gets there hell have a better chance of finding the prob as you say it occurs only when the heatings been on a while.. ask himto speak to his technical support manager too...

 

[gavinda]

if you're on contract..book your call then crank the heating up..when the eng gets there hell have a better chance of finding the prob as you say it occurs only when the heatings been on a while.. ask himto speak to his technical support manager too...