Constant air locks in CH circulating pump

[Pnb]

Hi,

Hoping someone can help me out or give me some advice with an issue I have had for a little while with my central heating and seems to be getting worse.

I have a standard gravity fed CH system in a two story house with F&E tank in the loft, boiler in the garage downstairs with a magnatec filter and circulating pump and two valves in an S plan layout in the airing cupboard on the first floor. Circulating pump is a british gas multihead and the F&E pipes join the pipework just before the pump.

My issue is that I am constantly getting air locks in the CH system which seem to be at the pump and the only way to clear is to bleed the pump via the screw in the middle which lets out air for approx 5 seconds followed by a surging noise in the pump and the water starts flowing. Once the water is flowing it is very noisy and sounds like its gurgling through the pipework in the airing cupboard. The system might run fine for an hour or so before it airlocks again and needs bleeding to let water flow around the system. When the airlock has cleared all the radiators heat up fine and the CH seems to work well. The pump itself is also very noisy when running.

Does anyone has any experience of anything similar or could suggest anything to check? Is there an easy way to check if the feed pipe could be blocked? Only thing I have noticed is that the circulating pump is at the highest point in the system other than the F&E pipes.

Any help would be much appreciated as its starting to drive me mad!

Many thanks.

 

[fixitflav]

Have you checked it's not over-pumping - water flowing out of the vent pipe above the F/E tank? Can happen due to blockage.

 

[Pnb]

Have you checked it's not over-pumping - water flowing out of the vent pipe above the F/E tank? Can happen due to blockage.

Ive had a look in the F/E tank and it doesn't appear to have been pumping over, although the water does look fairly mucky in there. Could it be sucking air in from the expansion pipe if it cant draw in from the feed pipe?

 

[ianmcd]

post a pic of how your pump is orientated, so many people get it wrong

 

[Pnb]

post a pic of how your pump is orientated, so many people get it wrong

This is a picture of the set up in the airing cupboard, please ignore the red circle around the bypass valve. Would the fact that the pump is inclined slightly higher at the bleed screw side create any issues with air getting trapped?

 

[45yearsagasman]

Use a magnet all around the cold feed/vent connections. If it sticks to the copper, you have a blockage/restriction. That 15mm cold feed is a likely spot.

 

[fixitflav]

View attachment 152809

This is a picture of the set up in the airing cupboard, please ignore the red circle around the bypass valve. Would the fact that the pump is inclined slightly higher at the bleed screw side create any issues with air getting trapped?

If I remember right, Grundfos say having the shaft slightly inclined, as yours is, is the ideal way, as it takes load off the bearing. Can't put my hand on the leaflet just now.

 

[lostinthelight]

Something I found:
It is preferable to install Grundfos circulators in a vertical pipe

pumping upwards. This position ensures that the pump shaft

is horizontal, which reduces the thrust bearing load and ensures

positive air purging from both the rotor chamber and impeller

housing.

Pumping downwards in a vertical pipe is not recommended as

this may lead to air locking of the pump, with resultant loss of

performance. However, pumping downwards is acceptable

provided an effective air vent is incorporated in the system,

before the pump.


Where pumps can only be installed in horizontal pipework, it is

imperative that the pump shaft is horizontal, or slightly higher

at the vent plug end.

The shaft must not fall below the horizontal plane, even by a

few degrees, as this causes premature wear of the top bearing

and shaft.

Pumps should not be installed with the shaft in a vertical plane,

as this may lead to dry running of the top bearing, noise and

possible pump failure.

To avoid cavitation noise and risk of damage to the bearings the

minimum pump inlet pressure should be 1.4m at 82°C (water

temperature).

 

[fixitflav]

Where pumps can only be installed in horizontal pipework, it is imperative that the pump shaft is horizontal, or slightly higher at the vent plug end.

That's what I was getting at.

 

[ianmcd]

your pump is fine so the problem is not there as @45yearsagasman suggests run a magnet around the cold feed and see if the magnet attracts to the copper pipe , if it does you have a blockage in there, it is the first fittings to the left of the pump in your pic were the 15mm pipe is in a U bend from the F&E tank and connecting to the 22mm pipe at the pump

 

[Pnb]

Thanks for all your help, I tried the magnet on the feed pipe and have got no attracting so fingers crossed that is clear. However I did take out the magnatec filter again last night to check it and it was pretty full of rubbish again, thinking the system needs draining and flushing through with some cleaner.

I did try isolating the pump this morning to take the head off and see if there is debris inside the housing causing it to be noisy but couldnt get one of the lock valves to turn so will try again when I can actually drain the system down.

 

[ianmcd]

try putting cleanser in and clean your filter every couple od days and see how much you can get out before draining and flushing and adding inhibitor, do not use sentinell x800 for this method