Hi,
If the boiler is leaking water at the rate you suggest and you cannot see any signs of water damage on your ceilings down stairs (which would suggest a leak from the pipework upstairs), then the leak must be from either the downstairs pipework (under the floorboards so you cannot see it) or from the 'Pressure Relief Valve' (inside the boiler). This valve is designed to releave 'over-pressure' in the boiler. However, the valve seat can sometimes become blocked with debris which prevents it from closing. Thus it remains in the open position which results in water constantly leaking from the boiler and you having to regularly top it up.
The Pressure Relief Valve dispences this water from a 'Discharge Pipe' which will be situated outside the house (which is probably the pipe you are seeing the leak from). It should be a copper pipe sticking out of the wall probably bent downwards and usually close to where the boiler is mounted. If you can see water constantly dripping or flowing from it then the Pressure Relief Valve is the VERY likely culprit! This is NOT a job you can carry out yourself. An engineer will probably replace the valve as cleaning and replacing only to find that the fault is still there is not cost effective for you or the engineer. However, you can keep topping up the boiler and have your heating on. Central Heating Boilers are designed to 'lock-out' if the system pressure is too low. This is there for your safety, but if the water pressure drops too low through the night, then the boiler will lock out and you're going to wake up to a cold house in the morning! Which in your present situation with a young baby, is far from ideal.
Unfortunately the problem will continue for as long as the valve is blocked. The valve will cost approximately £70 but obviously i don't know the specifics of your system or regional price variations. You could ring a local plumbers merchants and give them the boiler type and size etc and ask for a quote on a Pressure Relief Valve just so you have some idea. As for fitting time, you're looking at about an hour tops i would suggest and again, you'd have to check with your engineer for his hourly rate but the average is around £40-£50 an hour these days. We're not cheap i know but that's the rate 'up North', down in London its cheaper to see a Plastic Surgeon!
Hope that helps.
Sean, March 2006
