Cold radiators - air lock?

[JoeJoe]

The space under the floor boards exactly where the pipes run is completely open to the outside (well, to the space under the eaves that is the same temperature as the outside). It is a long story, but during the first winter after the builders who did our extension had left a couple of years ago I realised that they forgot to insulate the wall under the eaves (floor to about a metre high). I have spent many hours crawling there to put the insulation in place and was (wrongly) under the impression that the gap under the wall (space under the floor boards, so immediately under the wall) was left open intentionally to allow air flow (silly, I know). I should have fixed it, but never did...

I put a very simply diagram of the situation here:

temperature outside over night was -16c, so I suspect that freezing is still a possibility?

As to having an air lock:

It is very cold outside, and is likely to stay that way for a while. Apart from the three cold radiators both heating and hot water seem to be working fine, and we can comfortably leave the situation as it is for a while if needed.

I would rather not do anything that may result in loss of hot water supply and/or heating for the rest of the house.

My questions therefore are:

- what is the potential downsides of trying to remove the airlock by closing all the working radiators and after a while trying to bleed all the radiators (and possibly having to re-balance the system)? I really don't want to be left without heating/hot water in this weather...

- What is the downside of doing nothing for a while? Can it damage anything (boiler,pump,pipework, etc)?

Many thanks in advance for all the very useful advice so far.

[Weatherlawyer]

It sounds like you don't have enough water pressure. Though you say you have. I take it there is a scale in the control panel somewhere?

What is it reading?

[JoeJoe]

It sounds like you don't have enough water pressure. Though you say you have. I take it there is a scale in the control panel somewhere?

What is it reading?

There is a digital display that says 1.1 bar -

[BartC]

Hmm, it's not the clearest of diagrams... Is it some sort of isometric drawing?

The space between ceiling and floorboards above, while it might be vented to the outside, should be nowhere near the outside temperature, providing the house is heated. (And if it really can get that cold, then the pipes might need insulation, even if just to preserve the heat.)

But still, -16°C is about the same as the inside of my freezer... And even if it's 10° warmer in that space, -6° over a matter of hours might possibly have an effect.

If that pipe has really frozen, then it should fix itself when the temperature gets above freezing, unless the pipe has burst, then you will know because the pressure will drop (and you might notice some water around).

I did that once with one stubborn radiator, closing off all the others, so the water *had* to flow through that one. Although that wasn't a pressurised system. So perhaps leave one other radiator open (I think some combis have a bypass pipe inside, but I wouldn't rely on that).

With your particular problem, I might try and trace the pipes (feeling along them to see where they stop being hot), but that requires access.

(If I was feeling adventurous, I might even try loosening the pipe to the first cold radiator (after closing the valves on the cold ones) to see what sort of pressure there was. Or perhaps just try bleeding them (letting some water out) should result in a small loss of system pressure, if at least one pipe has some flow. With some ingenuity (closing one side of rads then the other), you might be able to test both outward and return pipes.)

If the other rads are working, then I don't see a problem. (But I'm not an expert, I just have bad luck with heating systems..)