An old cast iron boiler like that takes a lot of gas to heat it up when it turns on.
The when it cycles on again it has to reheat the cast iron block.
The efficiencies are quoted for a brand new boiler. After many years, the gas side gets all rusted up with poor heat transfer and the water side usually has a coating of lime scale which also reduces heat transfer.
My advice is to repair the boiler now and aim to replace it during the summer. The real cost could be less than £1000 saving on the BG price.
Tony
The when it cycles on again it has to reheat the cast iron block.
The efficiencies are quoted for a brand new boiler. After many years, the gas side gets all rusted up with poor heat transfer and the water side usually has a coating of lime scale which also reduces heat transfer.
My advice is to repair the boiler now and aim to replace it during the summer. The real cost could be less than £1000 saving on the BG price.
Tony