Combi boiler thermostatic mixer shower

[GEOFFH3]

I,m looking at installing a thermostatic mixer shower to bathroom. Combi boiler is in loft & water takes ages to come through hot.(has always been like this from new) Can i break into hot water pipe in loft & run a feed straight to mixer in bathroom which is almost directly underneath boiler.

 

[SimonH2]

You can, but it might not make much difference. Combis take time to fire up and heat up the primary circuit and hence the DHW. Thus you turn on a tap, and perhaps 30s later there is hot water leaving the boiler - the BG badged WB in my house can take a full minute !

This is a fundamental issue with combis - and there have been various measures built in over the years to "deal" with it. Some fire up every now and them to keep themselves warm. Some have a very small storage tank in the back of the boiler.

Before you want hot water, try this : turn the hot tap on and off again, ie just run it for a couple of seconds. Now wait 30s and turn the hot tap on - and see how long the hot water takes to come through. It'll probably be a lot quicker than from cold.
The first turning on of the hot tap triggers the boiler to fire up - and then most of them tend to stay on until they're hot. Then when you turn the tap on again, the boiler and primary circuit are already hot.