Topped up boiler 3 times in 3 days!

[HexBramble]

My valiant combi boiler has been losing pressure v quickly and I've just topped it up for the third time since Sunday. After a quick google, a potential leak was mentioned so I've felt under every radiator in the house and they are all bone dry.

Any advice please? My plumber charges £50 just for a call out

Could be a leak in a pipe, not the radiators. Could also be connected with the 'exhaust' pipe. We had both those issues on separate occasions - just lucky I guess. Not sure that this is a DIY job.

Could be a leak in pipe work under floorboards. Or something else completely.

Sorry but you need a plumber.

My guess is that it's what's called the pressure relief valve or pressure relief switch. That's something internal; my own Vaillant boiler did the same thing last year. Then, this past winter my brother's boiler (not a Vaillant)had the same problem - pressure relief valve again.

I don't think it's a massively expensive thing to sort out - getting the valve replaced is a quick job. Mine was done through insurance though, so I'm not sure how much it will cost.

Vaillant have a good helpline where you can talk to a 'technical adviser', I think they call themselves. They might be able to give you a rough idea.

Go outside the house and look at the wall behind the boiler. Does a small pipe come through the wall? Is it dripping?

Do radiatior pipes run under the floor?

We had to keep topping ours up and had an air leak in the expansion vessel. This produced the dripping referred too by PigletJohn. We first noticed we had a problem as the pressure gauge was no longer at it's usual 1.5bar when the heating was running, it was rising to 3bar and emptying the water outside. If it's a leak on a pipe I don't think it would do this.