Gas boiler, controls and prog/stat

Brilliant, cheers :-)

Why would it do that without the fan running? "Balanced" means equal input and output pressures.

I see the idea, but not all pipes are heated, nor next to a CH pipe. Therefore it's not something I would implement.

If you want to save the primary circuit from freezing then only a small amount of antifreeze is required to make the water turn into a mush rather than solid ice. If there's a concern over toxicity then propylene glycol can be used.

I'll think I'll stick to my programmable thermostat with its own built in frost setting of 5C.

There are 'old fashioned' balanced flue boilers that are not fan-forced. I suspect they are the most ineffient types going and ?most have now been recycled into Nespressos. I regularly see properties with a modern 4 inch balanced flue adjacent to a bricked up hole that was about a foot square where the old balanced flue came out.

Thank you . Couldn't remember which was which off the top of my head.

No they would be opened up by the room stat set much above freezing

In my case its in the corner of the integral garage. With a belt and braces approach I also have a greenhouse heater in there with a frost setting.

Yes, indeed. But the non fan-assisted flues required some thermal activity in the boiler in order to expel the products of combustion and draw in fresh air. There would be negligible circulation without that.

Are you sure? If the heating's on all the time anyway, there's no point in having a frost stat.

If the timer isn't calling for heat, the room stat won't do anything regardless of the temperature, and you'll be dependent on the frost stat.

Mine's avoiding getting recycled, 78.something% SEDBUK rating last time I looked, doesn't justify the spend to replace it