New boiler has resulted in increased Gas usage

sounds like your property is heating up quicker and looseing heat even quicker through cavity walls.
so the new higher output boiler is working hard to maintain an even temperature and burning for a longer time period.
turn down boiler thermostat.
your measurements of units is not an accurate way of calculation.

 

Today I have turned down the boiler themo by 1 notch and the room thermo to 20 degrees and will monitor the usgae over the next couple of days.

[your measurements of units is not an accurate way of calculation.]

It was the easiest way rahther than converting to KWH

 

After turning down the boiler thermostat a couple of notches and adjusting the TRVs down on the warmest rooms (kitchen, bathroom, study, dining room) and it still has been very cold in the toon over the weekend, surprisingly the amount of Gas usage has fallen significantly, from 5 units to 3.5 units. This is now very reasonable as the heating is on for 24hrs per day.
Thanks for all your advice.

 

The largest Apollo Fanfare is only 14.7kW, so a 37kW combi boiler will be more than adequate. Why did you agree to such a high output combi? Do you have a large house with several baths and showers running at the same time?

The installer should have set the max output for CH to meet your house requirements; obviously he has not done this.

 

I would say you are doing fairly well to be using only five units a day if your system is running 24 hours. Would anyone agree? We have our heating on approx four hours a day and use approx 4 units which I think equates to about 40kw.

 

[quote="D_Hailsham";
The installer should have set the max output for CH to meet your house requirements; obviously he has not done this.[/quote]

Boiler is fully modulating so you don't have to adjust the heating load you can however have the boiler start on less gas for heating (i.e have the gas valve open for say 75% rather than the 100% it comes set for out of the factory)but that is different from adjusting the heating load and most installers wouldn't even know how to go about this.

 

Which just goes to show that keeping your heating on 24 hours/day is more economical that just a few hours once or twice a day when the boiler spends all it's time getting the house up to temperature rather than just keeping it there.

 

no because
the heat loss at night is reduced as the room temp reduces

if you leave it on normal temp at night you have greatest heat loss all the time

if a boiler can bring the house up to temperature in one hour why would it be cheaper to have a boiler modulating all night!!!!

 

See http://www.diynot.com/forums/viewtopic.php?t=158935 for a discussion on the need to range-rate an oversized modulating boiler. The OP had a 38kW boiler with an overheating problem, which disappeared when the boiler was turned down to provide the required 24kW max output.

 

There is no scientific basis for saying that.

The rate of heat loss is determined by the difference in temperature between inside and outside. It has nothing to do with the rate the house is heated.

For a house to get warmer, the heat being produced by the radiators must be greater than the heat being lost through the walls, i.e the heating input must be greater than the heat output. Once the house is up to the desired temperature, all the radiators have to do is to produce enough heat to balance the loss through the walls.

The greater the heat input, relative to the heat output, the quicker the house will reach the desired temperature, which is why radiators are frequently oversized by 10-20%. This is OK if you have a working family and the house needs to be heated up for an hour in the morning and again at 5 or 6pm for the evening. But if a house is occupied all the day - retired people for example - then the over sizing may not be so important.

 

But you miss one essential thing.....the fabric of the building won't get up to temperature in one hour but if left on, and yes a slightly lower temperature is more comfortable, the building reaches a steadier state and thus the heat loss through the walls will be offset by not having to warm up the structure again and again.

 

the temperature off the building fabric cools much much slower and has a lot lot less influence on heating rate compared to other factors
this obviously ecludes the outside walls