How do I bleed a CH pump?

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spooky_b329

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Just drained and refilled my central heating after replacing a sheared off valve...(no leaks! :D )...my first bit of plumbing!

I've bled all radiators starting from downstairs but after running the boiler they remained cold. (conventional open system with tank in loft space) I then noticed the pump was very warm to touch but the pipes either side were cold, after some persuasion with a hammer the pump whirred into life, but the pipes either side remained cold.

Can anyone tell me how to bleed this pump? Its on a 15yr old Potterton boiler, I've felt all around the casing and can't find anything that feels like a bleed valve. I can't see the top of the pump without unscrewing the top cover of the boiler, but seeing as I can't feel anything I've not removed it so far.



Also, can anyone tell me what the switch does (red arrow) on top of the pump? I knocked it whilst trying to find the bleed valve, pretty sure its back in the original position but just want to check what it does...just in case :)

Thanks
 
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that is the pump speed
you can bleed the pump by removing the black cover on the front of the pump their is a nut underneath that.

have you no bleed valves on the end of a pipe in your airing cupboard. maybe next to your cylinder
 
Thanks for the quick reply...the cylinder is directly above the boiler.

The only valve on the pipework around the cylinder is on the pipe that is arrowed, its the same as the drain cock I used to drain the system behind the boiler. I assume this pipe is the cold feed for the cylinder as it comes down from the loft and into the base of the cylinder?

The two pipes on the right hand (EDIT: LEFT HAND!) side pass behind the cylinder and then to two vertical pipes travelling from downstairs to the loft...there are no valves on these that I can see...although there is that silver box with a switch labelled 'manual open' and 'auto' on it.

 
Oh and thanks for the tip about the black nut, I had unscrewed this but it didn't seem to want to come out completely, I'll be a bit more forceful with it ;)
 
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OK I've undone the nut again, I can pull it out about 5mm then it turns freely (feels like its turning the motor?) but there is no loss of air or water...
 
ok you can sometimes fre an airlock by turning the controls on full and the pump speed up to 3.

if not slacken one of the fitting to release air.
 
Depending on how hard you persuaded the pump the impellor may have sheared off of the motor shaft. Turn off both valves either side of the pump and undo the four allen bolts holding the pump head on. Then remove the head.

Make sure the impellor is intact and that it spins with power on.

James
 
Only some sharp but gentle taps...

Pipe from boiler to pump is now hot though it cools down a few cm from the pump, pump output is still cold.

Pump is getting warm, how bad is it to run the pump with no water in it?
 
Pump casing is now too hot to touch for more than a few seconds so I've turned it off.

Previous owners have left us with the remainder of their British Gas boiler and central heating cover...how likely is it that they'll find a way of charging us for something if I call them out?
 
Running a pump with no water in will do damage, but for a few seconds to check it, is fine.

A new pump is about £40-45 so i would check the impellor hasn't sheared off, and are you sure the pump is running. If it seems to be running but no circulation it probably has sheared off unless you have a big airlock but check pump first.

James
 
spooky_b329 said:
Only some sharp but gentle taps...

Pipe from boiler to pump is now hot though it cools down a few cm from the pump, pump output is still cold.

Pump is getting warm, how bad is it to run the pump with no water in it?
Click to expand...


your not running it without water it's just not moving. but don't want it to get overheated
 
Pump is definitely running, as I can hear it humming and it sounds like it is finding a trickle of water every now and then. Before tapping the pump with the hammer the casing was warm but the pump itself was silent.

Yesterday none of the pipes around the pump got warm, but today after turning the speed up the inlet pipe did heat up, very hot at the elbow behind boiler, then cooled down to just warm when it met the pump.
 
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