Myson Midas Gas Usage

[gary]

Potterton Myson Midas BF old combi natural gas boiler. At start up it uses gas at the rate of 90cuft per hour then drops back to 60cuft per hour. Over 1 hour it uses 70cuft. If my maths is correct 90cuft equates to about

28Kw. From the sedbuk site the spec for this boiler states "Power: modulating 20.5 - 20.5 Kw" Is the gas rate on the boiler set too high (I don't have the service manual for this boiler, so don't know what the rate should be)? Any help for my sister-in-laws huge gas bill appreciated! Gary

[Andy]

The quoted power rating may be its output power. If it uses 28kW to give out

20.5kW then it has an efficiency of 73%, not unusual for an older non-condensing boiler. My newish Vaillant has a SEDBUCK quoted efficiency of 78%.

Andy