On 03/02/2019 13:17:25, AnthonyL wrote:
The Baxi 105HE combi boiler is right at the back of the rear utility
room extension of a bungalow, approx 15m from the kitchen which is at
the front of the house and where the mains comes in.

The central heating is fine (touch wood).

Problem 1
=======

It is a real pain getting hot water to the kitchen. I calculate
there's 2.3l of water sitting in the pipes which has to be pushed out
before any hot starts to appear. And then 2.3l of hot being wasted in
the pipe when turning the tap off. Would you agree with these figures
and any suggestions?

For 15mm pipework I calculate just over 1l per m of pipe.

I have an undersink water heater. That does solve the dead leg of cold
water.

Problem 2
=======

It is very hard to get the flow right either to the kitchen or to the
bath (~9m from the boiler). Too fast a flow and the water is cold
(see later) and too slow a flow and the water again is cold. Try to
dribble it and the water might be hot but by the time the bath is
filled at that rate the bath is still cold. Any suggestions?

9m is remarkably long. Find a shorter route? Move boiler?

Problem 3
=======

This is a more recent phenonemon but the shower, which is in the
utility room hence near the boiler is generally fine but every now and
again runs cold in the middle of a shower. Only occasionally but it
causes a scream from SWMBO. Any suggestions?

Problem 4
=======

Turning on the cold water tap in the kitchen seems to deprive the
boiler of its hot water flow and causes it to run cold. Any
suggestions?*

I would check flow rate into the property and at a hot tap. The boiler
may have a spec on pressure drop across the heat exchanger and you
should be able to find the same for 15mm copper pipe.

Question 1
========

I am not understanding exactly what the temperature LEDs are telling
me. If I understand correctly the hot water is heated via a secondary
exchanger so the flame heated hot water is just going round and round.
Now are the LED's telling me the temperature of that water or the
water temp as it being delivered?

I wonder if I have the hot water thermostat set at optimum. The dial
is at "14 mins past". The LED shows 80deg. What happens if I set the
thermostat too high?

80C is very hot for hot water delivery.

* These bungalows, built in the 1960's, originally had their boilers
in the attic and thus fairly central to the delivery points (kitchen
and bathroom). Cold water was via a storage tank (still there for
cold in the bathroom). A separate tank was used for hot water and I
believe that it may have been heated both by the boiler and an
immersion heater. An Italian previous owner gave rise to the current
installation.

Thanks