Doctor Evil wrote:

Gledhill have changed the specification over the years of the
BoilerMate. Yours will have an internal DHW take-off coil. The new
models have plate heat exchangers. Is that so? It appears the
thermal store is struggling to cope after house extensions. All is
not
lost.

Indeed it does have the internal coil. Also has header tank as part of
the unit.

Q1. Does the store gives adequate showers in summer when the heating
is not extracting heat from the store?

Absolutely. Not had any problems in the summer at all.


Q2. How did it perform, in heating and DHW, before the hosue
extensions?

Thats a tricky one as the first extension was shortly after moving in.
Heating has never been a problem, just that DHW runs out during cold
weather. Noticed it mostly after second extension.


Q3. What percentage has the house increased in size?


Approx 15%

Q4. Does the boiler heat the store via an internal coile, or does it
heat the store direct (the same water in thye store and boiler)?


Its the direct type.

Q5. Is the CH taken off the store. Most Boilermates this is the
case.

Yes. Works well too.



Firstly:

a) I would replace the boiler with a larger boiler of approx 30kW
(twice the size of the extisting) with 28mm flow and return to the
thermal store. This will give a far higher recovery rate and be
heating up the store as water is being drawn-off.

b) Fit a blending valve on the boilers flow and return to ensure
only
75-80C water enters the store.

c) De-scale the DHW coil, as this may degrade performance if scaled
up. Ring Gledhill in Blackpool, they will recommend a solution to
de-scale.

d) Fit a flow switch in the cold DHW feed to switch off the CH pump
when DHW is called to prevent heat being extracted from the store to
the rads when DHW is being called. The flow switch can energise a
relay to cut out the pump. Simple to do.

If still not up to scratch, then do:

e) Have the flow switch also override the thermal store cylinder
stat
and bring the boiler in immedately DHW is called. You could put this
on a 20.30,40 second time delay to prevent nuisance boiler cycling.
This will pump heat into the store imediately, whereas if you rely on
the cylinder stat you would have lost 1/4 to 1/3 of you hot water
before the boiler starts to pump heat into the store.

Installing the above two points is not difficult or expensive and
saves
a wedge on a new store. This should cure the problem.

Further:
If the store is being heated adequately and the problem is that the
internal DHW coil is not man enough produce the hot water, which I
doubt from what you say, You can always retrofit a plate heat
exchanger
and pump for DHW take-off and use the existing DHW as a pre-heat, in
essence turning it into a hybrid heat bank/thermal store.


--
Doctor Evil

Thanks for the advice.
The other problem I have is that I want to relocate the store
downstairs. As it has a header tank attached, this is not possible
without ripping the header tank off and running a pipe up to the loft,
which i'm trying to avoid.