how to check efficency of new Gas Boiler ?

Got a new Gas boiler installed a few months ago as part of a new house extension. Installed four new extra rads onto system. Got gas bill and noticed massive difference between last years usage for this period (extra 3500 btus). Original boiler was 14 years old. I would have thought a new boiler would be a lot more efficient. Is there any easy way to test new gas boiler as regards if it is working correctly?

First you should compare the efficiency of the old boiler with the new one, check the sedbuk page. Then you should check the manual that comes with the new boiler and check what it says about the exact emission values. Then you should get e real heating engeneer or a good plumber to check the emission values with the proper measure instrument. If he/she says that you can't have a printout of these MEASSURED values-good by.
Who has connected the boiler? What does the meassure protocol/report say? It is absolutely necessary to meassure the emission values AND to hand out the written and signed report.
Once you have a real specialist in the house tell him to adjust the pump to meet the demand. A pump can be set at various levels, with just four rads and maybe a tank to feed, the lowest setting would be -most likely- the right one.This would avoid permanent start ups.The efficiency of the Sedbuk system shows the efficiency of the boilers at the stated output.So if your output demand is less than stated output at the boiler you'll get a ping-pong (smiley) rythm, on-off-on-off etc.. This will cause losses at the efficiency rating.
This could be overcome by using a "modulating" boiler. Better a "modulating condensing boiler" and if water mains pressure allows for it then a "modulating combi condensing boiler".
And of course the hydraulic adjustment at the radiators should be done as well, a real plumber would know what to do.
I explained the process here on AAM before, it can be done as a DIY project as well.
Comparing like with like you need to know the energy content in kWhs of the fuel, BTUs are an outdated but still used method to hinder comparison/competition. Check the SEI homepage for "fuel cost comparison" -BTUs aren't even mentioned any more on the fuel cost comparison sheet.

Heinbloed,

I checked manual under technical data for emission values. It was not mentioned anywhere. Could it be called another technical name?

Regards,

Suicra05

CO ppm, NOx ppm, CO2 %.
These must be stated in the installation & servicing instructions. As well a "Declaration of conformity" (as defined in I.S.813) must be provided on completion of the installation. A copy must be given to the responsible person(you) and to the gas suplier- if required.These are legal binding obligations.If your installer is not able to do so or not willing then report him to the authoritys, the health and safety department might be the right adress. A gas boiler not comissioned is illegal. If something happens no insurance will pay for damages.

To convert British Thermal Units to KWh, 1 BTU = 0.0002930711 Kwh. The BTU is still widely used in the US and occassionally in the UK (on older systems), although KWh is the SI unit used in most of mainland Europe and Ireland.

I would say experiement with the thermostat on your boiler, it wil lregulate the cycling of the boiler, if you set it too high the boiler remains on all the time. Tweak it until you have a trade off between gas usage (you can monitor the cubic meters of gas used on your meter outside) and the internal temperature. It might take a few tries to get it right.