Regarding a boiler repair package. Understand the difference between combi, system, and regular boilers. To help with any queries you may have about your quote we'll give you a courtesy call. Some properties won’t need the maximum flow rate, and in the case of a system that’s full of heating sludge, a high flow rate can increase back pressure, blowing the pump seals. White vinegar is often used in combination with bicarb to create a ‘fizzing’ action.