Constant bleeding!

[kernowman]

Just recently moved into a house with heating that is driving me nuts. Every day I go round with the radiator bleed key and let air out (assuming it is air not gas - not tested yet). Worst affected is the upstairs radiators, especially the bathroom (a tall chromed job) and the smallest bedroom which is close to the pump and above the boiler in the kitchen beneath. Above the pump/transfer valve is two air traps which always have air and even after bleeding several times a day I still hear air rushing round the pipes. Baxi boiler, Grundfos pump and expansion tank so nothing unusual there. Expansion tank has plenty of water and doesn't change level. House is probably around 20 years old although the heating looks updated since.

If air is getting into the system where would it come from? If it's gas surely it cannot make so much in so quick a time?

 

[ricarbo]

the pump could pull air in if it's set too fast, in certain circumstances, try setting to slowest speed. If the washer on the inlet side of the pump is faulty, it could also let air in, but would then leak when everything is off.
Got any records from the previous people?

 

[kernowman]

The previous owners were somewhat less than communicative as there was a divorce involved - much as we could do to get instructions how to disarm the alarm when we moved in

Today I tried the naked flame test on the escaping air and it definately isn't hydrogen so that's one cause ticked off the list.

I have slowed the pump down already a week ago to setting 2 as on the fastest speed it made some awful noises which suggests it now has a limited lifespan. Already bought a replacement pump should it give up the ghost altogether. Slowing the pump down has had no apparent effect on reducing the intake of air. Would slowing it down even more to 1 be worth trying?

I had thought the pump was gulping air due to a low water level but the pump is sited down level with the bottom of the hot water tank and the tall chrome radiator in the bathroom is hot above the pump's level.

 

[meldrew's_mate]

Does the cold feed from the F&E tank feed into the suction side of the pump, and is the pump the right way around (pumping direction towards any control valves?

 

[Slugbabydotcom]

pump could pull air in if it's set too fast

They can also drag air in through the pump itself when it's knackered

I did a post mortem on one guilty of this and proved it was happening as the inlet had typical black gunge staining yet from the impeller area onwards it was rusty red! proving air ingress

 

[kernowman]

Thank you for your thoughts gentlemen.

As usual the pump has been fitted into a position where I cannot actually see the flow direction arrow itself although it isn't physically fitted upside down. Directly above it is the flow control valve.

Seems like the pump is going to be the likeliest suspect in the air 'crime', so next logical step is to fit the new pump I have bought. It has isolation valves above and below so it's not too much grief to swap out.

 

[kernowman]

Incidentally, how is the water level in the heating topped up if it's low?

On the expansion tank in the loft I can see the ball valve, the overflow pipe and expansion pipe going over the side into the header tank, but I cannot for the life of me see where the water exits the tank to feed the heating system. There is quite a bit of muck in there and have felt round with my fingers but still cannot find another connection.

 

[kernowman]

Pump is definately fitted the right way, pumping towards the motorised valve. Have reduced the pump speed to it's lowest setting and doesn't seem to suck quite so much air in.

Found the feed outlet pipe - underneath the ball valve DOH! Cleaned the tank right out now so there is clean fresh water Pushed a length of tubing down the outlet to about 2 foot to see if I could clear any blocked muck. Beneath that is an isolation gate valve which is wide open as far as I can tell.

I suspect that there is still a blockage somewhere between the header tank as when I bleed the tall chrome bathroom radiator I never once have had any water coming out of it only air. Surely with the header tank around 5 feet above it then some water should come out?

 

[Slugbabydotcom]

Found the feed outlet pipe - underneath the ball valve DOH! Cleaned the tank right out now so there is clean fresh water Pushed a length of tubing down the outlet to about 2 foot to see if I could clear any blocked muck. Beneath that is an isolation gate valve which is wide open as far as I can tell.

I suspect that there is still a blockage somewhere between the header tank as when I bleed the tall chrome bathroom radiator I never once have had any water coming out of it only air. Surely with the header tank around 5 feet above it then some water should come out?

Could be that you are on to something there
Those feed pipes do sometimes block up but the blockage is usually at the bottom where it enters the system.
Where you say about not getting water out of your bathroom rad is often indicative of such a blockage.

Two ways of dealing with it

Drain the system and cut the pipe near the bottom. Clean or replace as necessary

Stick a hosepipe onto your vent [temporarily] and blow the blockage back up into the header tank with mains pressure. It's cheating I know but it does get your system working for now and it proves that a blocked feed was the problem.

Either way flush the system and add inhibitor afterwards