On 03/02/2019 13:17, 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?
The further away it is, the longer you will have to wait, and the more
water you need to draw off. Insulating the pipe run may help a little -
save it going cold quite so fast after last use.
The only real options for fixing it are providing a source of hot water
closer to the point of use. Perhaps a small under sink unvented cylinder
(which could be heated electrically or by the CH side of the boiler).
Alternatively a "on demand" electric heater just for the kitchen sink.
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?
The 105 appears to be a 30kW boiler... rated to give a flow rate of DHW
at 14lpm with a 30 deg C rise, falling to a bit over 10 lpm for a 40 deg
rise.
If you draw water through it faster than that, it won't be able to
achieve the same temperature rise. Some boilers include temperature
sensitive flow regulation - so that they can throttle the rate of
delivery to maintain a set temp. A Quick look at the specs on this one
does not suggest it has this. Hence in colder parts of the year you may
want to turn down the inlet cold water tap a little to limit the flow
rate through it to something it can get hot enough give its power and
the incoming water temperature.
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?
Ear muffs? :-)
It might be the shower is not using enough hot water.
At low flow rates the water temp will start to rise, and the boiler will
modulate its burner power to try and stay under the preset max DHW temp.
However there will come a point that it can't keep under this limit
without cycling the burner off. (it can modulate down to about 11kW
IIUC). So with a 40 degree temp rise that would imply a minimum flow
rate of: 11,000 x 60 / 4200 / 40 = ~4 lpm
So checking the head for scaling etc, or even changing the shower head
for a more "thirsty" on might help.
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?*
Is this new or has that always been the case?
Try throttling the cold flow rate to the tap with its service valve to
see if it helps. If it does then fitting a PRV inline with it may make
for a better (i.e. less noisy) fix.
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.
Yup its a traditional twin HX setup. A differential pressure flow switch
senses when the hot water is required. That switches a diversion valve
that directs the pump flow round the short circuit inside the boiler
that includes the plate HX rather than the external CH circuit.
Now are the LED's telling me the temperature of that water or the
water temp as it being delivered?
What does the user manual say?
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?
At low flow rates you get scalded.
* 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.
How much does it annoy you? Enough to fork out the significant cost to
fix it properly?
--
Cheers,
John.
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