On Sunday, 3 January 2021 at 16:25:19 UTC, Cliff Topp wrote:
John Rumm formulated the question :
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.
Just FYI if anyone is interested you can see photos of the setup he
https://drive.google.com/drive/folde...Zm?usp=sharing
or if that wraps incorrectly https://tinyurl.com/yabpmsco
Thats the arrangement we had frost stat and pipe stat and as Adam mentioned wired in series. If you did not have the pipe stat the frost stat on its own would keep the boiler running as in a garage, outhouse or loft the boiler firing up would do little to raise the temperature. Having the pipe stat setting the upper temperature for the return flow shuts the boiler down preventing continuous operation.
Richard