Air in Towel Rad

[GazKaz]

Hi all

Please be gentle with me, this is my first post!!

I have a 4 year old Central Heating System with a Glow worm combi boiler. Around 2 years ago I took out the bathroom rad and replaced it with a towel rad. Had no probs replacing re-charging etc, but after a couple of weeks I noticed the top of the towel rad got cooler. I checked the system pressure and it had not dropped at all. I can bleed the rad OK and the top gets hot again but the top cools again in around 2 to 3 weeks.

I left this in its current state and perseveared for about 2 years as I was getting no joy from my local plumbers merchant.

Since then I have put up a partition wall up in our bedroom, to create a small box room (which is now going to become a nursery!) and I had a friend who works for British Gas to install a small rad in the nursery. I asked him for his advice on my towel rad and he said it is just one of those things.

After he installed the small rad in the nursery he re-charged the system but he also put in some Sentinel x100 inhibitor as I had none in previousley. The small rad now gradually cools near the top over about 3 to 4 weeks!!

So, (sorry for the long post) I have a towel rad that cools at the top (about 3 rungs) over 2 to 3 weeks and a new small rad that cools strangely from the top left hand side to the right!

I don't like ringing my British Gas friend as he did it as a favour, but through all this I'm not losing pressure at all.

Thanks in advance

Gary.

 

[Bas]

I might be corrected but the air in the system has to come from somewhere, it might be coming in from a leaky valve somewhere (you would expect to see a wet carpet) or being sucked in from a vent pipe or it might be gas created by corrosion, I think you need to look for some more clues

 

[GazKaz]

Hi Bas

I don't think I've got a leaky valve as I have no wet patches anywhere near the rads, and also I'm not losing any pressure from the system.

I can't see it being corrosion as the system is only 4 years old.

When you say it could be getting sucked in by a vent pipe, which vent pipe do you mean?

Thanks

Gary.

 

[Bas]

just re-read its a combi - not vented then so no vent pipe - sorry.

You can do a small test on the air you take out of the rads. Hold an upturned tumbler over the bleed valve during bleeding and try and light the gas... if it lights its corrosion I think. There are lots of threads here if you search on the subject.

 

[oilman]

You don't have a vent pipe as you have a sealed system. Have you checked the expansion vessel pressure? I don't expect this to have much to do with your problem, but the system should be set up correctly before you start digging. The air pressure should be set with zero water pressure. Then set the water pressure. Search the forum for October 2003, lots of expansion vessel info there.

I am coming across information that corrosion inhibitor can cause problems in certain circumstances. The system should be cleaned before the inhibitor is put in, even then there can be problems. I need to do more reading about this. There was a long argument (er...discussion) on the forum recently about a similar problem.

One thing that is difficult with a sealed system is moving enough water to carry the air out of the pipes. If you connect a pressure regulator in the filling loop, you can set the pressure at say 1 or maybe 2 bar, and then have a continuous supply that will allow you to open the bleed valve and run off a litre or two of water to drag the air along the pipes.

Not saying that this will cure it of course.

 

[ChrisR]

Have heard similar rumours about adding inhibior. SHould call Sentinel and Fernox to ask them.

4 years is time for loads of corrosion. We see new rads holed in 6 months.

 

[oilman]

ChrisR, my understanding so far is it's something to do with sodium molybdate, and it needs something else to stop it attacking the metal.