On 02/01/2021 16:44, Cliff Topp wrote:

What is the relationship between the controls on the boiler itself, the
thermostat/programmer in the hallway and the heat in the rooms?

On a traditional setup, the stat on the boiler will set the upper limit
on the flow temperature of the hot water produced by the boiler. With
old fixed output boilers that basically means it runs flat out until the
primary water exceeds that temp, and then cuts power to the burner
(while still running the pump) until the temp falls.

With more modern modulating output boilers, they will aim to set the
flow temp to that limit by adjusting power to match the actual load. If
the load is too small that its unable to modulate lower, then they
revert to the style of operation used by fixed output boilers.

Our previous boiler was an Alpha CD32C and the boiler controls for both
heating and hot water were numbered from 0 to 9, and both were set to
No. 7. The thermostat/programmer in the hallway was only rarely set to
above 18C. Only on the very coldest days of winter would we have to put
it up to about 20 or 21C.

In a perfect world, the stat in the hall ought to keep the place feeling
the same regardless of how cold it is - it would just run the heating
more frequently to compensate for the higher rate of heat loss. However
as you have discovered, that does not always work of the boiler can't
heat the place fast enough on cold days.

(this is where weather compensation systems can be used to ramp up the
flow temperature on the boiler in sympathy with the external temperature)

Our new boiler is a Worcester Greenstar 30i and instead of the boiler
controls being numbered 0 to 9, the readout is in actual degrees
Celcius. Both heating and HW are set to 56C but I don't know if that was
set at the factory or if the installers set it.

Probably set by the installers. Also probably a bit on the low side on
cold days unless you have oversized radiators.

(54 degrees is the *return* temp at which you get a notable improvement
in condensing efficiency for the boiler)

We are finding that 18C on the old stat/programmer in the hallway was
more than comfortable for us but the new stat/prog has to be set to at
least 20C or 21C to 'feel' as warm as it was before.

I don't know what the *actual* temp of the rooms is as we don't have a
standalone thermometer, but it's weird trying to get used to this new
system.

You will probably need to set the temp for the rads on the boiler a bit
higher during the colder parts of the year. 56 will be fine for the
"part load" months.

On top of that, and perhaps even more importantly, is the frostat.

The old Alpha boiler was up in the loft for 14 years and as far as I
know it never had a frostat connected - unless it was factory-fitted and
integral to the boiler itself but definitely no external unit was wired in.


See 5.8 (7):

https://www.alpha-innovation.co.uk/c...%2010%2005.pdf

"7.Explain to the User that an internal frost thermostat is fitted in
the boiler, and that the electrical supply to the boiler must be left on
for the thermostat to operate"

The new installation *does* have a (Honeywell) frostat wired in and it's
keeping the heating on all night, irrespective of if I turn the hallway
stat/programmer down to a very low level or completely off. This is
really bad in three ways:

1. Extra gas used equals bigger bills
2. Even though the rads are only lukewarm to the touch, we aren't used
to *any* form of heating on at night and it's making it difficult to sleep
3. The pipes and rads creak and groan a lot which is making it almost
impossible to sleep!

Any advice?

Well firstly a frost stat *should* override any others - its there as a
failsafe. However the greenstar also has an internal frost stat:

https://www.worcester-bosch.co.uk/su...20811923/12545

It might be that the installers were worried that the pipework in the
loft would cool faster than the boiler - but that seems unlikely since
the boilers one kicks in a 8 degrees.

ISTM that the external stat has been wired incorrectly or set at too
high a temperature. Since the boiler has its own internal stat, I would
be tempted to simply disconnect the "call for heat" from the frost stat
and see how that works.

--
Cheers,

John.

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