Turn your preheat option off on your combi boiler!

Not all combis have a pre-heat facility, and others have a switch on the front panel.

It hardly wastes a 'massive' amount of gas. Well insulated tanks lose very little heat - A 100+ litre hot water tank with water @65C will only lose approx 2kWh in 24 hours. In any case where does the lost heat go? it warms the house.

Another factor for those of us with water meters is that the cost of the water wasted while waiting for warm water to emerge is probably greater than the 'wasted' gas. Don't forget that water(+sewerage) costs a minumum of a penny for every 5 litres(over 2p in some areas)

Probably a sensible compromise is to switch it off over night or when away from the property - then the noise of the boiler switching on for a few seconds won't disturb.

tony4563 wrote: »

Combi boilers don't have tanks, do they?

Some have a small internal tank which holds pre-heated water.

The idea being that when water is demanded at a tap, there is a shorter delay before the hot water emerges - and hence less cold water to run off.

I was making the point that if a 100+ litre HW tank only loses about 2kWh worth of heat in 24 hours(say 6p), how much would a little tank in a combi lose?

rogerblack wrote: »

Small tanks will use more to keep hot than you might think.
A 10l tank has a third of the surface area of a 100l one.
In addition, there is likely to be thinner insulation on it, meaning the loss may well be half that of the big tank, even though it's a tenth of the volume.

Small tanks will use more to keep hot than you might think.

Also in some pre-heat tanks, the water isn't kept hot by the boiler firing, but with a small immersion heater at ??? per KWh :eek:

Some of the Worcester boilers allow you to set the operation of preheat (via the internal timer) to periods when you're likely to need hot water. For me this is the best compromise

First off the pre-heat option is not used for instant hot water, they are used to provide high flow rates. The water from the pre-heat tank is added to the normal mains water hot water flow to get a greater flow rate so that these boilers can run more than one tap/shower at a time.

I measured mine with the pre heat on 24/7 and then off. The preheat tank 18 lites in my case used 30kwh per week so 1560Kwh per year or about 50 quid a year at current prices.