Advice needed for very old house

J30

And how long is it likely to take for the walls to “fill up” so that is retains the heat inside better?

Netexporter

As long as it takes. As I have already said, my old house took about a fortnight, but the walls were about half a metre thick. A brick wall is about half that.

J30

Netexporter said:

As long as it takes. As I have already said, my old house took about a fortnight, but the walls were about half a metre thick. A brick wall is about half that.

I do appreciate your advice so thank you. Is it likely to be affected however if I turn the thermostat down overnight?

Netexporter

The smaller the difference in temperature between the air and the wall, the slower the heat transfer. Everything naturally flows downhill; heat, water, electricity... The bigger the gradient, the faster the flow.

J30

Netexporter said:

The smaller the difference in temperature between the air and the wall, the slower the heat transfer. Everything naturally flows downhill; heat, water, electricity... The bigger the gradient, the faster the flow.

Am curious to try this out I think what concerns me is the boiler working flat out trying to get up to temperature 

Netexporter

You either pay for the gas, or you can be cold. It's your choice.

J30

Netexporter said:

You either pay for the gas, or you can be cold. It's your choice.

It’s not all about the paying for gas that concerns me. What concerns me is the boiler working flat out without a break - and how long it can cope before packing up - as it is depending on the thermostat temperature 

Netexporter

Working flat out is better for the boiler than constantly cycling. Less thermal stress on components.

MultiFuelBurner

It's been -2oC here all day and although not gas out heat pump has been running constantly 

We will use about 36kwh today due to the temp outside and that's in a modern EPC B house and we won't be turning it off overnight or setting a min temp or 14oC.

You probably need to go through the pain of heating the fabric or the house up fully and not setting the heating back so much overnight as you will always be playing catch-up.

QrizB

J30 said:

Netexporter said:

You either pay for the gas, or you can be cold. It's your choice.

It’s not all about the paying for gas that concerns me. What concerns me is the boiler working flat out without a break - and how long it can cope before packing up - as it is depending on the thermostat temperature 

The boiler will be fine. The amount of heat it can put into the system will be limited by the ability of the radiators to emit it. Once it drices the rads as hard as it can, the return temperature will rise and the boiler will modulate down to match, or cycle if it can't modulate that low.

Which leads me on to asking: what model of boiler is it? How big is your house, how many rooms/radiators, and do you know the rads power ratings?

If you don't know the rads ratings, it's fairly straightforward to measure them, look at their design (one panel or two, fins or not) then find a similar rad at eg. Screwfix or Toolstation and work it out.