Air surfing around the central heating system

[ceecjc1]

Hello,

I have a question which hopefully you guys will have a logical answer to!

I moved into the house six months ago. The oil-fired, vented central heating system is about twenty years old and I plan to potentially replace it with gas this summer, but it's working fine for the time being.

I'm aware of the various causes of air in the system and in the last six months I've had to bleed the bedroom radiator (the highest one, I would guess) only twice, and none of the others ever have air in them. It's not a big problem but my question is as follows:

The pump makes a rushing sound every 5-10 minutes or so when it's running, but it's fairly quiet otherwise. This suggests the air bubbles are surfing round in a group when I would expect them to get caught as they float to the top of the first radiator they come to.

I've searched online and in these forums for the answer to this but can't see any similar questions, so apologies if it has already been discussed. Basically, physics would suggest that the bubbles should float to the first radiator they come to rather than continue round the system repeatedly until finally settling in the highest radiator.


(the alternative explanation is that the highest radiator is also the first one next to the pump and the air is being drawn down the overflow and then going straight into that radiator every few minutes, the cycle being coincidence).

Cheers,
Chris

 

[footprints]

As you suggest this is one of the good old favorites on forums because there are so many possible causes, one that springs to mind is the pump sucking in air through the open vent often just as the pump kicks in.

It "Surfs" around the system dude, till" like it wipes out man" and goes up the vent or feed till it can "ride another wave" from the pump starting

If you have a header tank in the loft you can try this, look in the tank and get someone to turn on the system for a few minutes then off watch the water level. It might bob a bit but should not do anything dramatic.

If water gushes from the open vent (the pipe terminating over the tank but above the water level) you have pumping over, if not get a container (old milk container will do) fill about 2/3 full with water and hold it up over the open pipe till the end is at the bottom of the container. Get you assistant who by now will have got bored and wandered off, to repeat the on / off as before. If all or most of the water gets sucked up into the pipe your system is sucking in.

Both point to a problem with the feed / vent either poorly installed or most often partly blocked.

Also look to see if the water is very black or rusty in appearance.