Boiler cuts out

[monkeyboy67]

I have a Baxi Solo 2 boiler. I have had some trouble with my central heating system for a while and now seem to be chasing my tail. Problem: the central heating runs for about 20 minutes and then the boiler/pump stop. Rads upstairs are piping hot, 4 of the 5 rads downstairs are hot too, the last one is warm but cooler than the others. The boiler stops before the room stat should cut in. Fitted a new pump yesterday (set to speed 3), no leaks, cleared a partially blocked line from the pump to the F&E tank. All rads bled well, hot water tank air bleed ok. I have tried removing an air lock if there was one by: closing both valves on a rad fitted with a drain tap, open drain then open either one of the valves (but not both at the same time). I have even tried back filling the system by fitting a hose to the same rad and filling until water runs out of the overflow pipe on the F&E tank. Once things have cooled down the (several hours later) the heating comes back on albeit briefly. Help, help, help!

 

[Slugbabydotcom]

Ok so you have one rad that doesn't warm up as well as the others and that should be sorted with a little balancing of the system. Search this site on balancing.
After that there is no law that states the boiler must run constantly.
When the system water has reached the set temperature by the BOILER STAT the boiler will shut down thereby saving you some money on gas and preventing the boiler from boiling it's contents. The term 'boiler' is actually a misnomer as it should never actually boil the water!
Your room stat will turn the boiler off when the room temp. reaches the set level. This again saves you money on gas and prevents the house from overheating.

 

[MANDATE]

You don't happen to have a 3 port mid position valve in your system, Sometimes these function ok while HW and CH is being demanded, but when HW is satisfied and the demand is for CH only they fail. usually due to a faulty motor or microswitch.
Of course if you have not got such a valve you can't have that problem. but the fact your heating was on for 20 mins I thought it may have been sharing with HW.

 

[Slugbabydotcom]

Went to one job recently where the boiler ran for a while warmed the rads got hot then stayed off for much longer than it should have done letting the house get cold. It was only after I eventually managed to get the room stat cover off to check the wiring that I realised that it was fitted above a radiator!!!

 

[monkeyboy67]

I have shorted the room stat out so as to elimate a problem with this. The stat is on the stairs so isn't getting any direct heating from a rad or other heat source. The rads are stone cold overnight and appear to get warm in the day so maybe it is something to do with the 3 port valve Hot water CH demand?... however I have a honeywell which I can manually open and leave open thus allowing flow through to my rads, I do this and it still mis behaves? Any clues

 

[MANDATE]

I thought that when you open the valve manually, the lever rests on a latch and holds the valve in the mid position for filling purposes and there is no latch to hold the lever in the CH only position.
Also if you can move and hold the valve in the CH only positon, the valve has to operate a microswitch to get power out of the orange wire to feed the boiler, as the alternative source of power to the boiler via the cylinder stat as been switched off. (HW satisfied or turned off)
I had a valve with a faulty microswitch so there was no power to the boiler when CH only was called for. But by calling for both HW and CH, the CH was ok providing I ran some hot water off, which meant the valve was in the mid position and the power to the boiler was supplied via the cyinder stat. Could this be your problem.
The key questions are: does the valve move to the CH only position? and if it does, why is there no voltage on the orange wire?, cause if there was boiler would function.

 

[arundel gas services]

you say the cold feed was partly blocked are you shure that the pipe it tees into is not also partialy blocked an indication of this is to try a magnet against it as the magnatite that causes the blockage is ferrous

 

[monkeyboy67]

Thanks guys, I really appreciate your time... I think with youur help we have narrowed the problem, with the divertor valve manually locked (not sure if its mid way or not) I get heating when there is a demand for hot water. Put the valve on auto and I still get HW but no CH....