Boiler turn off

[leesonr]

I have very simple 28mm gravity HW system to an indirect HW tank and a pumped 22mm CH system, with 15mm T offs to the radiators. The boiler is a balanced flue Potterton Kingfisher II approx. 10 years old. There is very little to go wrong with these boilers, though I recently replaced the thermostat, but it functioned perfectly afterwards. The boiler is now turning itself off before the flow pipe of the 28mm HW has even got hot, but the 22mm CH pipe is so hot you can't put your hand on it - the CH system is turned off i.e. the pump isn't running. The heat goes beyond the check valve, which should stop gravity feed of hot water to the radiators when the CH system is turned off. I tried running the CH system, which funtioned OK and the radiators heated, also the HW pipes heated and heated the water in the tank. I turned off the CH system and everything seamed OK for a day or two but now the problem has returned. Any one have any ideas what the problem is?

 

[kier]

is there water in expansion tank.
if yes possible blocked cold feed.air lock on primary flow hopefully not a blocked return pipe [rare]

 

[chrishutt]

Agree with above post. Also it is common for anti-gravity valves to jam up with crud. Quite likely that your whole system needs cleaning/flushing.

 

[leesonr]

is there water in expansion tank.
if yes possible blocked cold feed.air lock on primary flow hopefully not a blocked return pipe [rare]

Thanks for that. I'm pretty sure the expansion tank has water in it. I checked it about 2 months ago. I wouldn't have thought a 28mm pipe would block and what could cause an airlock. The system has always been difficult to fill since I had a loft extension and they resited the expansion tank and instead of having a separated vent pipe which it had before, they ran the vent pipe off the expansion tank pipe that tops up the system. I have to fill it from a pipe attached to the boiler drain cock otherwise the system won't fill without airlocking.

Is there a simple way to get rid of an airlock without draining the sytem?

 

[leesonr]

is there water in expansion tank.
if yes possible blocked cold feed.air lock on primary flow hopefully not a blocked return pipe [rare]

Thanks for that. I'm pretty sure the expansion tank has water in it. I checked it about 2 months ago. I wouldn't have thought a 28mm pipe would block and what could cause an airlock. The system has always been difficult to fill since I had a loft extension and they resited the expansion tank and instead of having a separated vent pipe which it had before, they ran the vent pipe off the expansion tank pipe that tops up the system. I have to fill it from a pipe attached to the boiler drain cock otherwise the system won't fill without airlocking.

Is there a simple way to get rid of an airlock without draining the sytem?

I've just checked the expansion tank and find that the water is down to the outfeed at the bottom of the tank. The ballcock had stuck! The rad in the bathroom which is T'd off the HW feed to the HW cylinder is full though. Any suggestions on what to do?

 

[croydoncorgi]

Yes -overheat the boiler. If (AND ONLY IF) you're confident about the feed and venting arrangements of the system, this will purge any air out of the gravity system. If you don't know how to do this - you probably shouldn't do it. For this to work and in any case, there needs to be an open vent connected to the top of the gravity flow pipe. Your previous posting suggests this may have been interfered-with.

 

[leesonr]

Yes -overheat the boiler. If (AND ONLY IF) you're confident about the feed and venting arrangements of the system, this will purge any air out of the gravity system. If you don't know how to do this - you probably shouldn't do it. For this to work and in any case, there needs to be an open vent connected to the top of the gravity flow pipe. Your previous posting suggests this may have been interfered-with.

There is a 22mm pipe going up into the loft area that is t'd off the 28mm flow into the HW cylinder, but because of the layout of the tank area, I can't see where it comes out. Surely there must be a vent on this sytem?

 

[leesonr]

Yes -overheat the boiler. If (AND ONLY IF) you're confident about the feed and venting arrangements of the system, this will purge any air out of the gravity system. If you don't know how to do this - you probably shouldn't do it. For this to work and in any case, there needs to be an open vent connected to the top of the gravity flow pipe. Your previous posting suggests this may have been interfered-with.

I've found out where the 22mm vent comes out it feeds into the cold water tank. So the system is vented. Presumably overheating the boiler involves interfering wit the normal thermostatic turn off of the boiler.

 

[croydoncorgi]

In a word, and for a few seconds of boiling only, yes.