Had a valiant 937 combi installed less than a year ago. But when you turn the hot water on it can take up to 30 seconds for hot water to come out. The engineer who installed it says that the boiler is coming on when you turn the hot water tap on so the delay is down to the length of the pipe. The diverter valve was replaced but has not really improved things. Putting the pre heat on or off doesn't make much difference. The boiler even has a built in tank but it takes longer than my friends whose boiler which has no tank. how long should you have to wait for hot water..?

Brendan, August 2011

the length of pipe is NOT a joke this length of cold water in (the hot pipe) has to be run off first.
if the combi is in kitchen next to sink you will have a very short length of cold water (in the hot pipe) to run off before the hot water arrives
if on the other hand the boiler was mounted in airing cupboard or even the loft you will have HAVE a larger amount of cold water to run off as the pipe length will be a lot longer but the bathroom taps will get it quicker as closer to boiler .
known as the dead leg part of the circuit

wirecutterman, August 2011

The length of pipe sounds like a joke!
There is a filter on the mains incoming on the boiler that gets blocked up very easily, It is relatively easy to remove and check as its only a fine metal mesh filter.
It normally gets blocked with a green lime scale.
P.s, i would get another plumber

bill, August 2011