Radiator needs bleeding every day

qsk

One of my radiators (highest of the house) needs bleeding every day and there is always air coming out. This has been going on for weeks.  I examined surrounding area and could not see any leak. The boiler pressure does not show significant drop. The pipes were cleaned in the summer and refilled.

Anyone got any idea what could be the reason? Could sludge in the radiator causes this (this particular radiator was not cleaned)? Thanks.

rob7475

When the system was refilled was inhibitor added? If you drain a bit of water from the system it should run clear after a few seconds - is that the case? If the water is brown you may have a build up of dirt/rust.

The air coming out could be hydrogen which is created when there's corrosion in the system I believe.

qsk

rob7475 said:

When the system was refilled was inhibitor added? If you drain a bit of water from the system it should run clear after a few seconds - is that the case? If the water is brown you may have a build up of dirt/rust.

The air coming out could be hydrogen which is created when there's corrosion in the system I believe.

Thanks for the reply.
Yes, 2L of Sentinel X100 was added to the system. The water comes out from the radiator (after air) is clear.
 

Bendy_House

Hi qsk.

The boiler pressure doesn't show any drop? What's the pressure set at? And does it vary as the system heats up, and then cools down at the end of the eve?

This is a 'sealed' system, so it's difficult - tho' not impossible - for air to get in to this system from 'outside'.

About the only way I can think of (actually the only way that comes to mind) that air can get drawn in to such a sealed & pressurised system is if the atmospheric air pressure is somehow higher than that of the system - ie the system pressure is lower than atmospheric. That would take some doing, but is not impossible. For instance, if you have your system pressure set at around 1 bar or slightly below, and the pressure gauge is on the ground floor, then that tells you that the system pressure is 1bar above 'atmospheric' at that level. However, the system pressure on a third or fourth floor could well be waaaaay below 1 bar, approaching zero (I think), and there then could be circumstances where the action of the water flow could cause an actual below-atmospheric pressure scenario occurring within the pipes on that higher floor. So, if there was a way for air to get drawn in, it ain't impossible...

But, far more likely it's one of two other possibilities; the first, as pointed out by Rob, is internal corrosion. Ie, a radiator is rusting from within. This would produce hydrogen, I understand, and not air, so if you are brave enough, you could try igniting the gas the next time you 'bleed' For this, an essential piece of equipment is a video camera, so's we can all watch.

You have had your system cleaned, tho', so corrosion is surely unlikely, at least to the extent of causing that much 'air' - that would be some serious corrosion. Also assuming that inhibitor has been added afterwards.

So that leaves, as the most likely scenario, a failed Expansion Vessel. This will most likely be located inside your boiler, and is a large flattish vessel which has a rubber diaphragm inside, with the system water (and pressure) on one side of this, and pressurised air on the other. The idea is that, when the boiler heats up, the system water expands and needs somewhere to do, if it isn't going to make the system pressure soar. The excess system water goes into this EV and starts to press against the diaphragm. The dia moves to accommodate the water, and squishes the air on the other side. The system pressure therefore stays pretty steady. When the system cools down, the contracting water comes back out of the EV, and the pressure - again - remains constant.

A common failure of the EV is that the rubber dia leaks, and that would allow the compressed air to go in to the system water.

If that is the cause, then at some point (when the EV runs out of compressed air...) you will notice the system pressure will be starting to drop when you bleed, and will also notice the pressure start to climb quite obviously as the boiler comes on from cold.

A new EV - if that's what it is - costs around ~£100, and is usually quite easy to replace. On some models, tho', it's located behind the boiler, so a major headache. In this case, you'll have the option of fitting an external EV somewhere else on your pipework, if you have room.

So, what to do? If your boiler is on the ground floor, and if the top rad is on a third or greater floor, I'd be inclined to try increasing the system pressure to a higher-than normal 1.8-ish, just to make sure it isn't a case of the top floor pressure being too low.

Or, test that bled 'air' next time - see if it's hydrogen (you will want to know if it's corrosion...)

Or, just keep truckin', and watch the pressure gauge. If it starts to fall when you bleed, but then starts to very obviously climb when the boiler gets the system hot, suspect the EV.

[Deleted User]

Tip from our boiler service guy, if we have a leak that is difficult to track down, tie some kitchen roll around the rad valves and see if they are soaking any water up. He reckoned sometimes the leaks can be enough to annoy but not enough to show properly. Especially the valves with green under the lock shield caps or TRV,

grumbler

half_empty said:

Tip from our boiler service guy, if we have a leak that is difficult to track down, tie some kitchen roll around the rad valves and see if they are soaking any water up.

It's not a leak, it's the opposite.

Bendy_House

But still a good tip

qsk

Thanks all for the kind advices.

The boiler pressure is 1.2 when cold. It increases to about 1.8 when running in full power. It was serviced over a month ago and was given all-clear (At the time, it was still warm and the radiator problem did not show up yet).

The boiler is a Bosch and still under warrantee. But I guess I need some more concrete evidence to call them out to look at the EV?

At this stage, I feel that rusts causing hydrogen is the most plausible explanation (the radiator is about 18 years old). I guess I should wait under summer to have it checked/replaced (Albeit hassle-some, it is still working and I don't want to disturb its working order in this cold weather).

grumbler

You can try collecting the gas when bleeding the radiator. If this really is hydrogen,  you can trap it into an upside-down tin can. Then... https://www.youtube.com/watch?v=Rfl6vgq7EIA

Bendy_House

That's scary!

A less dramatic way would be to hold a container - an empty can like that - upside-down over the bleed screw so's the hydrogen - if that's what it is - floats up and in to the can. Keep it upside-down and place it on a table. Light a taper, and then turn the can over - you should just have a brief blue pulse if it's H2.

Personally, I don't think it's H2 from rust. For a start, there seems to be too much of it from what you describe. And also, surely whoever cleaned your system added inhibitor?

I think more likely is a leaking EV. The system pressure already rises from 1.2 when cold to 1.8 when hot, which is of 'interest', although not critical. (A well set up system would ideally only fluctuate by, ooh, 0.2 bar or so, but some do vary by more).

What to do? Leave it and keep monitoring it. By all means try the H2 test. But what I expect will happen is that the 1.2 bar figure will start to drop when you bleed the rad, which may then require you to 'top up' the system, and the upper 1.8bar figure will also likely increase as the system becomes hot. NB - if it starts to reach the mid-20's, then you need to call someone in.

Check your boiler warranty - see if the EV is included.

Bendy_House

https://www.youtube.com/watch?v=LKBEWdwjEAc