Radiators no longer getting very hot

[raljon]

I would be grateful for any advice on a CH problem which appears to be getting worse.

First things first..system is Potterton Kingfisher 2, RS 60 boiler, gravity water fed , pumped CH. Primatic cylinder. Radiators: 3 largeish, 4 small, grundfoss 3 speed pump.

The radiators no longer seem to get that hot and the system now takes about 1hr 15min to reach operating temperature. System seems well balanced but heat is not really there.

Have looked at boiler heating up and have observed that the flame is roughly on for 2 mins and then off for 1 min even from cold. Should the flame be lit continously while it is warming up? (The boiler stat and room stat are set to max). I have also noticed that whilst the flow pipe gets very hot the return pipe gets only luke warm even after 1 hour. Flame burns blue and looks good. The pump sounds as if it is working ok and you can hear a change when the speed selector is altered, albeit faint, (I have it set on 3). I have removed each of the radiators and reverse flushed them in the garden. Some black sludge came out but system now clear. I assume I cant use system corrosion inhibitor because of the primatic tank so will have to flush every other year.

Can anyone suggest how I can get the radiators to feel like a little more than cupboard heaters!!!

Many thanks

This problem seems to be 'creeping up on me' I am sure it is worse now that it has ever been. Two of the radiators were added by me last year to complete the system. After some difficulty balancing them all I remembered the system as working ok if a little slow.

 

[Rob]

Listening to the pump is no way of telling if its working. Either take it out and check or just replace it.

 

[namsag]

Heat is not getting away from the boiler so either pump has gone or you have a partial blockage somewhere.
From cold boiler would be on at least 15 mins non stop for heatin

 

[twgas]

I would look for an anti-gravity valve, on the heating flow, if there is one it could be blocked or jammed.

 

[raljon]

thanks for your suggestions..they all make sense to me. Would the anti gravity valve be the small cylinder in the pipe just after the pump and about 2" long? Also does anyone know why it is covered in green and white 'fur' on its outside? Are these items generally standard fittings and easily obtainable from plumbing shops? thanks again

 

[namsag]

How many pipes do you have coming from the boiler (ignoring gas) 2 or 4

 

[raljon]

How many pipes do you have coming from the boiler (ignoring gas) 2 or 4

4 in total

 

[namsag]

Anti gravity valve is about 2 inches long and brass l(looks like a big socket) usually on the flow pipe within about 2 foot of the boiler and pump is usually on the return.
These stick in the part open position and form a blockage so it may well be your problem .
A sharp tap with a hammer can free them but if yours is leaking etc i would not try that . they cost a fiver from plumbcentre etc
22MM anti -gravity valve the new ones are a slightly different length from the originals and are usually spring type so you may need to alter pipe a little if they dont have exact type.
And the chances are your pipe is 3/4 inch and as diy , to save soldering cut out a bit of pipe and use a 22mm socket . Some will say get 3/4 olives but i personally have never had a problem with using 22mm olives

 

[raljon]

thanks Namsag...I took a chance and hit it hard with a hammer. Guess what...its fixed!!! Where do I send the cheque?

thanks to everyone...it pointed me in the right direction