Help needed with central heating / freezing pipes

This is the frost setting. They will open when the room starts to get very cold.

Again correct.

No, but make sure that all the pipes are lag properly[1]

No it can freeze during the day and the night.

Yes leave it on minimum setting.

In very cold conditions ie below -3 the building should be check daily for problems anyway.

-- zaax

Yes, but check your insurance. You may find you are not covered for burst pipes unless the premises is frequently checked. Draining down maybe another option, but rather few systems are designed so they can be completely drained down (and this is not just the heating system, but all the supply pipework too).

Is there a room thermostat anywhere?

That article is too simplistic to hold any validity -- ignore it. In any case, it isn't talking about frost protection setup.

You should get an electrician to fit a frost stat (which shouldn't cost much), and then leave the boiler on 24 hours, with the thermostatic radiator valves in their normal positions and the boiler temperature set to minimum, with the frost stat controlling the system. The frost stat should be put in the place most likely to be the coldest in the building, but where it isn't going to be directly heated by a radiator or any associated pipework. Set it to something like 6C, or for an old building with solid walls, you might need to go up higher to prevent a damp smell. Any pipework running through unheated areas of the building must be well lagged.

Thanks Andrew

Thanks Zaax

This will be our last winter in the house and money is tight so we don't want to go to the expense of fitting a room thermostat if possible although it is a good idea.

I set the boiler temperature to minimum and the 3 radiators to the 'blue snowflake' setting aboy 4-5 hours ago. Now I have a few more questions:

1. The boiler seems to be going crazy switching on and off every few minutes, is this normal for my settings?
2. Despite the radiators being set to 'blue snowflake' setting 4-5 hours ago. I just checked and two of the radiators are so hot you would not want to touch them for long and one of them is luke warm, is this right? I would have thought they would get just warm enough to stave of freezing pipes rather than a heat up really hot / cool down cycle. Could someone confirm what should happen? (present conditions are very cold in the rooms).
3. I bled all the radiators, one of the radiators had a lot of air in it but I expect they have not been bled for a long, long time. Am I ok to do this as I assume this is a closed system.
4. The pressure is about .75 bar, is about right for the above mentioned settings.

Thanks for all your help

Regards

Pete

Yes -- you need a room stat (or frost stat) to prevent the boiler firing up when there's no requirement for heat from the radiators. Otherwise, the boiler will just be keeping the bypass loop up to temperature, which is going to result in frequent switching on and off. (For this reason, boilers fitted nowadays _have_ to include some mechanism such as a room stat to switch them off when there's no call for heat, to avoid wasting this energy.)

You might find it cheaper to get a room/frost stat fitted, than paying for this energy usage and possibly a replacement gas valve or igniter, or whatever part of the boiler wears out faster as a consequence.

Oh, and I'm assuming the boiler does have a bypass. If not, then you should have one radiator with no TRV or other means of closing off.

What are the temperatures in those rooms?

Yes, I would expect the radiators to be hot at the top, as they will have the full temperature boiler water there. Unless your boiler is a condensing boiler, the minimum flow temperature is probably something like 70C. However, if the TRV has reduced the flow to a minimum, you'll find the radiators get cold as you run your hand down to the bottom, because the flow in the radiators is tiny. This is how the TRV reduces the heat output from radiators.

Pressure would typically be about 1 bar when cold (and it goes up when the system gets hot, but probably not by much in such a small system). The .75 bar will drop when the radiators are cold, and there's a risk it might drop below the point where the boiler will operate (assuming your boiler has a pressure sensor switch).