Had a new combi boiler installed a month ago. I have to top the water up a few times since then. The plumber is going to try a sealant, but if it doesn't work, we will have to find the leak. My question is this: do I expect the people who fitted the boiler to look for the leak free of charge as it presumably a result of them installing it, or will I have to pay, on the grounds that it might be an increase in water flow that has produced the leak?