1 rad always needs bleeding, pressure always drops.

[richie2305]

Hi,

The rad furthest away from the boiler (400mm ground floor at front of house), always seems to be collecting air so that it needs bleeding weekly as it goes cold, this also means the pressure drops by approx half a bar in 2 weeks so always needs refilling.

The boiler (first floor back of house), is a sealed system combi Worcester Bosch 24i RSF and has been in 3 and a half years.

Things I have done:

Replaced 3 TRV's as wouldn't switch rad off.
Checked every fitting and tightened carefully, no leaks were found anywhere or residue of scale to indicate leaks.
Replaced the heat exchanger as clogged up due to being a hard water area.
Replaced the AAV as old was dripping, opened the screw half to 1 turn as required to let it do its job.
Drained/refilled constantly no sludge in system and its running well and quiet.

Has anyone any ideas of how to spot where the air is gettig in or how the pressure is dropping?

The only other thought I had was the PRV, but put a container under the pipe on a very rare dry day and no sign of water leak, should I eliminate this anyway?

Also is relevant that the rad is the furthest away from the boiler?, could the air collect there for some reason (even though the problem is elsewhere) or does it suggest the problem could be in that area as I thought the pump may push the air round and vent at the AAV.

Any help would be greatly appreciated.

 

[Bahco]

Sounds like you have a leak somewhere on your system.

Go over it with a tooth comb.

 

[richie2305]

Is there any obvious way of checking for leaks, bar the obvious ie water or scale from dried water.

If leak can't be found this way is it worth eliminating the PRV as I am thinking if the leak is that slow the water may evaporate rather than drip out of the pipe.

 

[gas4you]

Pressurise boiler and isolate at f & R valves under it. Leave it as long as you can. If pressure does not drop then leak is on the heating system its self.

 

[richie2305]

Trouble is the leak is quite slow so would not notice for a while I presume, unless I hang fire until it gets warmer, I have left the inhibitor out until now as sick of replacing it but could put some in til then.

If it is the PRV or in the boiler say shouldn't the AAV expel the air, or does that depend if the pump gets hold of the air first and send it round the system?

 

[easyflow]

0.5 bar sounds quite alot in 2 weeks whick does sound like a lead.
Dont know what size your system is or how it was put together, but pressurised systems with lots of compression fittings tend to suffer from micro leaks where compression cuplinks elbows etc leak without notice.
Using LSX compound around the olives reduces micro leaks and presurised systems hold pressure better.

 

[richie2305]

Could be worth a try, I have always been concerned with compression fittings and olives etc, with how much to tighten and whether to reuse on same olive.

The system is 9 rads and a towel rad (3 bed semi average size house), all soldered fittings really except the obvious radiator fittings which are compression, also mostly in/around the boiler itself.

Should I go over all joints, as like mentioned before I can't see any obvious leak.

Thanks.

 

[uknokianut]

I had a job where the leak couldnt be found and the customer was topping up the system every two days, went all over the system looking for the leak, but it wasnt on the system, it wasnt the prv either. Finally checked the heat exchanger to see water in the tray below but the high temperature of the flames was evaporating it before it showed up.

 

[richie2305]

I replaced the Heat Exchanger a couple of months ago as boiler kettling and hot water virtually stopped, I have checked this since and is ok, the air was getting into system before I changed this and I hoped this would cure the problem (maybe creating gas or something), how wrong was I.

The water evaporating was my only hope of it being something like the PRV where I might not see any residue of water.

The DHW now flows better than ever, and CH works fine apart from this, but being the person I am I just want to rectify it and get some inhibitor back in the system then forget about it.

 

[bengasman]

In that case you would do well to get a RGI in and check the whole lot over