Air in radiator

[kerr]

First of all hello, first post on this forum,

I have a problem with my central heating system, its a conventional baxi burmuda gas back boiler, with hot water tank upstairs and the central heating system has its own header tank.

The problem I am experiencing is that one of the radiators needs bleeding about once a week, because its full of air - this rad is the first in the circuit I believe.

This has been going on for months even a year or so, I have drained the system a couple of times to repair poor joints in the past, each time thinking this may have been the cause..but no

where can the air be coming from?, there are no signs of leaking in the system, I have tried different pump speeds etc

If I have to bleed that rad' much more I feel I am going to crack!

Thanks in advance

Kerr

 

[Gas2Air]

If you have no micro leaks then your pump/cold feed configuration is wrong. The pump is causing negative pressure around the system thus sucking in air via the vent pipe. An air-sep and repipe is required.

 

[kerr]

Thanks for the reply

Sorry for my stupidity, but could you explain a little more.

the pump could be causing negative pressure, possibly sucking in air from the air vent, where is the air vent situated?

how do you go about making the pipework good, to include the separator?

Thanks

Kerr

 

[kevplumb]

is the pump on the return

 

[kerr]

Yes I beleive it is

Kerr

 

[kevplumb]

your system is under negative pressure
it pulls the water round instead of pushing it (pos pres)
if you have a small leak in a valve say
it will tend to pull air in than leak water out

 

[kerr]

Just gotta find the offending valve right? - or are there additives that can be used?

no signs of leaking (when not pumping or not being used in the summer) unless the ruddy thing is under a floor.

Kerr

 

[kevplumb]

look for signs of leakage ie green colour scale etc
i had one in my last house bathroom rad was getting the air it was the kitchen rad that was duff

 

[croydoncorgi]

In fact, some part of any open-vented CH system will be under 'negative pressure' (ie. suction) relative to atmospheric pressure. Has to be, because the pump sucks as well as blows!
With a 'microleak' such as you may have, the trick is to start looking on the inlet side of the pump (eg. pump union, isolating valve compression joint and gland, and so on, back through the pipework on both the CH and HW sides of the system.
If you've already done this to no effect, it's also worth checking that what's in the rad is definitely air. With the curtains out of the way, and with 'air' in the affected rad, open the bleedscrew a little and try to light the gas that comes out. If it lights, it's hydrogen and you need to start looking for electrolysis problems not microleaks!