Do they offer an after sales service? You have no items in your shopping cart. Our handy calculator makes calculating system efficiencies and generating package labels easy! It’s much more likely that your central heating system has a leak. Did you know that improper sizing of your boiler can make your unit run less efficiently and wear out prematurely? The costs for replacing a boiler will vary, but a straightforward oil boiler replacement plus thermostatic radiator values will typically cost.