UKC

There is one radiator in our house - well, actually it's the towel rail in the bathroom, but it's still basically a radiator - which seems to need bleeding roughly once a week. The top three or four rails turn cold within that time. The towel rail is the highest radiator in the house, but even so this doesn't strike me as being normal, so I wondered if the collective UKC consciousness could shed some light on to why it might be happening?

We did have to have the pipes feeding the towel rail replaced last year, after having had no heat out of thing for many months. They are plastic pipes, which we think is because of the awkward location of the towel rail (the feed pipes are buried in the plaster, behind tiles, in a location partially obstructed by a bath which is a very snug fit along the walls on three sides). The old pipes were found to be full of gunge when removed, but the plumber who did the job wasn't clear how they could have got that way.

At least we do now have a warm bathroom and dry towels, but I am worried that the continual build-up of air in the towel rail may be a symptom of the same problem that ended up blocking the pipework before, and that we may end up having another hefty bill to replace them all over again. It's also a little inconvenient having to bleed the towel rail so frequently, since access to the bleed valve is rather restricted and there is a distinct risk of rounding off the square actuator for the bleed valve if you're not careful to engage the key snugly before turning it.

So: any UKC plumbers got any helpful suggestions/ideas?

In reply to Martin W:

If at all possible, fit an auto bleed valve.

The bedroom radiator in my old house always used to collect air - never got to the bottom of why, by we're talking much longer timescales than you are.

It is possible to fit a catchment trap somewhere else in the system, usually low down, that allows you to collect and dispose of the muck, but it's more a workaround than actually fixing the root cause of the problem, which sounds like air is somehow getting into the system. Have you checked the header tank is full (depending on system)?

In reply to LastBoyScout:

Yes, the system is letting in air, and the problem needs to be solved at source (could be something with pressure/pump), rather than simply bleeding the air frequently. ... because it's potentially disastrous, in that the water becomes acid and starts corroding the inside of the radiator. If the water which dribbles out of the bleed valve when you bleed the radiator is at all black, you're in trouble, because that's oxide from the inside of the radiator and sooner or later it will burst. I had a problem with a house in Derby where the system was drawing in air and I had about 5 radiators bursting within about 2 years. Eventually the insurance would not pay up any more, and the whole central heating system had to be drastically redesigned.

In reply to Martin W:

As the other lads have already stated, it could be a system design issue. What kind of system do you have? If the pipe work isn't configured properly then it could be dragging in air, oxidising, etc blah blah.
If it's an open vented system could you post a picture of the cold feed, open vent and pump?

In reply to Martin W:

Is it a combi boiler?

In reply to Martin W:

You could try turning your pump down a notch. It could be pushing the water through the system to fast and forcing water into the expansion tank, thus then sucking in air.

In reply to Martin W:

I'm sure there will be a proper plumber along in a while, but in the interim I'll have a stab too...

It might be hydrogen coming out of your bleed valve, not air. This is a product of corrosion, as is black sludge. A corrosion inhibitor should stop that. There is a simple test to determine whether the gas is hydrogen, but don't blow yourself up.

I am not a plumber.

In reply to Turdus torquatus:

Just you leave it to the professionals pal....

In reply to Martin W:

My best guess is that the pump seals are going and air is being drawn into the system. The towel rail is collecting the air because as you say it's the highest point in the system.

In reply to Martin W:

Is it a closed system? Could be a leak somewhere?

Thanks all for your input and suggestions. A couple of points:
- It's not a combi boiler;
- AFAIK it is a closed system. There's a wee valve near the boiler for re-pressurising the circuit, but as far as I can tell repeatedly bleeding the towel rail doesn't cause the circuit pressure to fall - which seems odd to me.

I'm not sure that an auto-bleed valve would fit. The existing bleed valve lives behind a cosmetic cover which I don't think we'd want to have to do without.

I'm sot sure how to turn the pump down, but I can look in to that.

I think I can guess how to test for hydrogen being bled off - I can give it a go (carefully).

The pump seals is something I will keep in mind to mention to the professionals if the problem continues.

In reply to Martin W:

Does it have an expansion vessel fitted, usually a big red thing?

If you have check the pressure, not of the system (there'll be a dial for that, but of the bladder inside.

If this is low then what happens is the system heats up and water expands and leaks out somewhere, usually valve heads or at the pump or somewhere were you can't see it. The system then cools down, everything contracts and the system then such air in, usually from the same places it leaks out viola, you get air in the system.

I'd check this first.

Do you lose pressure if the heating is off also?

In reply to Martin W:


Why not fill a balloon with whatever gas you are bleeding off the radiator and if it floats then chances are it could be H2.

Then you can take the balloon outside and light it (from a distance for confirmation)