radiators not heating

[nothot2012]

The two radiators furthest from my boiler are not getting hot. The boiler is a potterton profile 60E.
I have motorised valves controling heating and hot water. hot water is working fine. I have checked the pump and the motorised valved and they are all working fine. When the boiler fires up the water in the pipes immediately after the pump and motorised valve gets hot very fast as do the first few radiators. But before the rest of the house heats up the boiler turns off. The heating is controlled by a room stat in the hall and this is not what is turning the boiler off. The hall is still freezing cold and I have changed the room stat just in case - this did not resolve the problem.
If I turn up the boiler control thermostat the boiler immediately starts up again, but cuts out before the far radiators are hot, even when turned to maximum. I am thinking that the boiler control thermostat is not working and is cutting out the boiler before the room stat gets a chance to.
Can anyone suggest any other possible causes or confirm that my suspicions about the control thermostat are correct? do the control themostats stop working and would that cause these problems. also, is replacing it a big job?
Any help would be much appreciated

 

[Burnerman]

Have a look at the FAQ's on radiator balancing....this effectively forces the hot water around the complete heating circuit.
The lockshield valves are the ones to adjust - usually 3/4 to one turn on from fully off is sufficient.
John

 

[nothot2012]

Have a look at the FAQ's on radiator balancing....this effectively forces the hot water around the complete heating circuit.
The lockshield valves are the ones to adjust - usually 3/4 to one turn on from fully off is sufficient.
John

Thanks for the quick response. I have tried the rebalancing, I got some heat to the radiators not previously heating up by shutting off all the other radiators. then gradually reopened them to rebalance. BUT the boiler is still switching off and on repeatedly and the temperature in the house is not getting up to the temperature set on the room stat. so this has sort of partially worked as a temporary fix. but the heating is still not functioning correctly. Can you suggest anything else?

 

[UnhappyChappy]

You might have loads of sludge in the central heating water that limits flow to those radiators. You can have the water tested to see how bad or good it is.

 

[nothot2012]

You might have loads of sludge in the central heating water that limits flow to those radiators. You can have the water tested to see how bad or good it is.

i've run some sludge remover through it and the water has come out surprisingly low in sludge, I was hoping it would cure it but its hasnt. The water leaving the boiler is v hot, and the first few metres of pipe, through the pump and the motorised valve heat up really quickly and get too hot to touch within a few minutes. ( i can access this pipework easily) But the heat still isnt getting to the far radiators before the boiler turns off. If I turn the boiler control thermostat up then the boiler lights up again but only for a short time. then its on and off every few minutes. could it be the boiler control thermostat is faulty> does anyone know how to test it?

 

[UnhappyChappy]

Just Google "free central heating water test". There are companies that do it by post.

 

[Nige F]

Pump might be on it`s way out - if so replace with a grundfos 15/60

 

[nothot2012]

Pump might be on it`s way out - if so replace with a grundfos 15/60

The pump is only 4 years old and is a grundfos 15/50. It seems to be functioning fine , I have tried all three speeds and I can see the pump spinning when I remove the cover screw. It also sounds fine.

A plumber came out and fitted a new boiler control thermostat but this has made no difference.
When he installed the new part he did not attach the copper lead to the side of the boiler casing ( because he broke the clips removing the old one) and he did not properly replace the rubber grommets that should be fitted around the copper lead where is passes through the compartments of the boiler. When I questioned him about this he said neither of these was particularly important, which I find hard to believe!

The boiler still cuts out before the house is fully warm, i.e. well before it reaches the temperature on the room thermostat.
Before the new part was fitted I could get the boiler to restart almost straight away by turning up the boiler control. thermostat - this would make it run again for a few minutes.
Now the new boiler control thermostat is fitted it will not restart the boiler and there is no audible click when I turn up the setting. I have to wait a while and then the themostat will click and restart the boiler. Anyone got any ideas??

Or can anyone recomend a good boiler engineer in the stockport area?