Have to keep bleeding rads on sealed system

[metaman]

Had an old tank central heating system converted to a sealed combi system in mid November, we kept the existing pipework and radiators.

Since then I've had to bleed the radiators every 3 or 4 weeks as the tops of the upstairs rads were noticeably cooler than the bottom of them.

When I bleed the rads, the boiler pressure drops to almost zero, where it's usually at 1.5 bar. So I top up back to 1.5. There isn't any noticeable pressure increase while the air is in the system however.

Surely this isn't normal, as I thought I would only be bleeding radiators once or twice a year with a sealed system?

Can anyone explain what it going on, or what I can do to solve it?

Cheers.

 

[muggles]

Was any other work done at the time? Were any chemicals added to the system? It could well be corrosion causing the air (actually gas) to form

 

[metaman]

Hi.

All we had done was all tanks taken out, conventional boiler taken out, combi in + pipework removed/added where needed.

Had Worcester's magnetic filter installed, and new bleed valves on all the rads.

System was flushed with cleaner, and Fernox F1 put in as inhibitor.

The engineer did say it was pretty badly sludged up when they flushed the system.

 

[ScottishGasMan]

Depends very much on how badly its still sludged up and corroded. Next time you bleed one, very carefully bleed it slowly, and hold a lighter carefully up to the bleed point very carefully, if the gas escaping from the radiator catches fire, quickly close bleed point off or smother with a wet cloth then close off, and contact you rinstaller as you still have heavy corrosion causing a hydrogen build up in the system, but do be carefull when checking.

If it blows the lighter out or simply appears to be just air blowing against a flame then your looking at sourced of air ingress, which wont really happen on a sealed and pressurised system unless theres a leak somewhere.

Now, before you bleed the rads, do you check what the boiler pressure is at? worcsters will notoriously run on systems with no pressure (not good for them but they will do it)

and what possibly could be happening, is that you have a leak downstairs under a floor, very slight leak but its there, your boiler pressue will then drop down to near nothing at which point air gets into the system and makes its way to the upstairs rads (as previously said because the worcster wont shut off till its too late)

 

[metaman]

I haven't done this test yet, but I can say that there hasn't been any pressure drop. It's only after I've bled them that I need to give it a top up.

 

[45yearsagasman]

Do the test and come back.

 

[metaman]

Done the test.

It seemed like a bit of air came out to start with, then it lit, but I'm not sure if I just couldn't tell that it had lit at first as I only had the valve open very slightly.

 

[JohnD]

When you clean the filter, how much dirt do you get out each time? Do you clean it weekly or monthly?

Is the amount of dirt reducing?

When a new boiler is fitted to an old system, it is essential that it is thoroughly cleaned. This may take half a day's work so bodgers may omit it. This will invalidate your boiler's guarantee.

 

[ScottishGasMan]

The simple fact is if it lit at all then you have hydrogen bulding up in your system due to metals in the radiators corroding due to incrorrect and incomplete flushing. Get your installer back as said it will invalidate your warranty and at the rate you appear to be building hydrodgen at must be corroding pretty rapidly