Running just one radiator

The_Earl_of_Streatham

I have a combi boiler which the spec tells me can modulate down to just over 7kW (Bosch Greenstar cdi 32, if it helps). I would like to run a single 2kW radiator for much of the day and only heat other parts of the house during the evening. I suspect this is likely to entail the boiler cycling on and off quite a lot. Will this shorten the life of the boiler or have other deleterious effects ?

I'm not really worried about the waste involved in pumping hot water across the house all day. My electricity costs six times as much as gas so I think I can live with a bit of inefficiency in that department.
Any views, experience or warnings most welcome, thank you.

[Deleted User]

How will you control the temperature of the single room?  If it is by thermostat, then you need to ensure that the system has either an automatic bypass or that a radiator in another part of the house is left fully open. Running a pump on a closed circuit will lead to pump failure: the circulating water has to go somewhere. Frequent boiler cycling will wear out components such as the pump and the fan in the longer term.

To answer your specific question. Your boiler is far too big for what you have in mind. I am guessing that it was sized based on your requirement for hot water not heating. If you want to avoid damage to the fabric of your house, then leaving the heating off all day in closed off rooms will lead to problems such as condensation and mould. I owned a property with Evohome eTRVs for 4 years and we found that room temperatures below 13C were just not sensible.

You also need to bear in mind that a cold-soaked room needs a lot of heating to raise the room back to a comfortable temperature. It follows that a lot of what you save closing rooms off, will be lost when you want to re-occupy them. My advice: go for a structured approach. Do not allow rooms that you intend to occupy at times during the day to fall below 13C (15C is better if you want quick re-heating). Rooms that are rarely occupied can be set at a slightly lower temperature but do not leave them without heating for weeks on end.

Lorian

check that your boilers controls support the modulating down mode - many dont.