I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

The old system was CH controlled only pump and HW controlled only boiler
which meant that the boiler was live most of the day (or twice daily)
with only one or two potentially brutal power offs mid-flame.

The new thermostatic control has the potential to do this sort of
unfriendly cut to the power feed several times a day. Apart from setting
minimum cycle time to 15 minutes is there anything else I can do? I
suppose it wouldn't bother a gas boiler so much.

Obvious fix being a relay to hold mains on until the boiler fan stops
drawing current (but that requires a modification to the boiler).

The advantages of smart start to match target temperature is largely
eliminated if I have to set the boiler to come on at some God forsaken
hour of the morning just in case the CH pump thinks it needs to be on.

Incidentally why don't these smart controllers provide decent manuals in
English with more sensible boiler and pump control outputs?

--
Regards,
Martin Brown

On 19/03/2014 10:12, Martin Brown wrote:
I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

Most boilers these days have a permanent live and a boiler on.
You need to check and use the boiler on not just switch the mains on and
off.

On 19/03/2014 10:12, Martin Brown wrote:
I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

The old system was CH controlled only pump and HW controlled only boiler
which meant that the boiler was live most of the day (or twice daily)
with only one or two potentially brutal power offs mid-flame.

The new thermostatic control has the potential to do this sort of
unfriendly cut to the power feed several times a day. Apart from setting
minimum cycle time to 15 minutes is there anything else I can do? I
suppose it wouldn't bother a gas boiler so much.

Obvious fix being a relay to hold mains on until the boiler fan stops
drawing current (but that requires a modification to the boiler).

The advantages of smart start to match target temperature is largely
eliminated if I have to set the boiler to come on at some God forsaken
hour of the morning just in case the CH pump thinks it needs to be on.

Incidentally why don't these smart controllers provide decent manuals in
English with more sensible boiler and pump control outputs?


I don't quite understand what type of overall control system you now
have. I assume that the previous system had gravity HW circulation and
pumped CH?

Is it now fully pumped? What have you got in the way of motorised zone
valves - presumably either 2 x 2-port valves (S-Plan) or 1 x 3-port
mid-position valve (Y-Plan)? What controls the pump? In a fully pumped
system it would normally be connected in parallel with the boiler's
switched live - unless the boiler required pump over-run, which seems
unlikely in your case.

By 'smart controller' do you mean a programmable room stat? What make
and model? The instructions are often a bit cryptic, but you can usually
fathom them if you read them a few times.

I don't know a lot about oil-fired boilers, but my Honeywell
programmable stat does have a mode with a longer minimum 'on' time for
use with oil boilers, but it still isn't *very* long. You must surely be
able to turn the boiler off when it's firing, when all demands are
satisfied? If not, there's little point in have a 'smart' control system!
--
Cheers,
Roger
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checked.

On 19/03/2014 15:22, Roger Mills wrote:
On 19/03/2014 10:12, Martin Brown wrote:
I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

The old system was CH controlled only pump and HW controlled only boiler
which meant that the boiler was live most of the day (or twice daily)
with only one or two potentially brutal power offs mid-flame.

The new thermostatic control has the potential to do this sort of
unfriendly cut to the power feed several times a day. Apart from setting
minimum cycle time to 15 minutes is there anything else I can do? I
suppose it wouldn't bother a gas boiler so much.

Obvious fix being a relay to hold mains on until the boiler fan stops
drawing current (but that requires a modification to the boiler).

The advantages of smart start to match target temperature is largely
eliminated if I have to set the boiler to come on at some God forsaken
hour of the morning just in case the CH pump thinks it needs to be on.

Incidentally why don't these smart controllers provide decent manuals in
English with more sensible boiler and pump control outputs?


I don't quite understand what type of overall control system you now
have. I assume that the previous system had gravity HW circulation and
pumped CH?

HW is still gravity feed and has to be as a heat dump for the back
boiler on the wood burning stove (previously for a Baxi grate).

Yes. With provision to override the pump and have it switched on with or
without the boiler if either the wood burner thermostat or a manual
switch requests it. This means you can have a fire and run the CH
without the oil boiler running at all sometimes. The wood burner with
its back boiler is powerful enough to more or less shut down the oil
burner except on the coldest winters days.

Is it now fully pumped? What have you got in the way of motorised zone
valves - presumably either 2 x 2-port valves (S-Plan) or 1 x 3-port
mid-position valve (Y-Plan)? What controls the pump? In a fully pumped
system it would normally be connected in parallel with the boiler's
switched live - unless the boiler required pump over-run, which seems
unlikely in your case.

The layout remains the same hot water is gravity fed (pump not on) and
CH is actively pumped. Boiler and hot tank are close together. No zone
valves entire house is either heated or not depending on the pump.

Hot water tank insulation isn't the greatest so leaving the boiler live
results in occasional wasted firings keeping the hot water hot. More
importantly being a fairly chunky oil boiler it is fairly noisy and the
rural house very quiet so it is annoying to have the thing come on any
earlier than is absolutely necessary in the morning.

The oil burner is a Worcester Danesmoor 15/19 I'd guess from about the
mid 1970's from the thickened computer style font on the control panel.
The only manual I can find online is for the model with the same name
which looks internally nothing like mine although might well have the
same quirks as Bosch recommend their own controller and setting it to
"G" so that hot water (boiler on) is always demanded when CH pump is on.

Unfortunately with no wiring diagrams anywhere and zero documentation
for the actual vintage model trial and error isn't very appealing.
Although less daunting now that spring has sprung than in mid winter.

By 'smart controller' do you mean a programmable room stat? What make
and model? The instructions are often a bit cryptic, but you can usually
fathom them if you read them a few times.

I mean one that calibrates itself to the thermal inertia of the house
and fires the boiler at the appropriate time(s) to hit the specified way
points on the temperature profile at its thermostat.

The model installed is a Heatmiser RC1-WTS rev 1.0
zone 1 = CH (room thermostat) and zone 2 = HW.

It functions but it seems to be abusing the boiler...

I don't know a lot about oil-fired boilers, but my Honeywell
programmable stat does have a mode with a longer minimum 'on' time for
use with oil boilers, but it still isn't *very* long. You must surely be
able to turn the boiler off when it's firing, when all demands are
satisfied? If not, there's little point in have a 'smart' control system!

You can but it doesn't shut down at all gracefully since it should
switch off properly with a purge of exhaust gasses rather than just
stopping dead as all mains is suddenly removed. It didn't seem to be a
bother it with the old once or twice a day basic controller but then a
fair proportion of the time it wouldn't be flame active when dropped off
power since it would happen at the end of an hour or so with the house
or hot water probably full satisfied and the boiler up to temperature
already in its standby state rather than active.

The new controller is pretty much forever switching the boiler off when
the flame is lit and the boiler isn't at all happy with it's lot.

Mention of the permanent live and switched live in an adjacent response
has given me something to look for, but I think this unit may be so old
as not to make the distinction.

--
Regards,
Martin Brown

On Wed, 19 Mar 2014 10:12:16 +0000, Martin Brown wrote:

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What do you mean by that? You say "old oil boiler" is it a gert lump
of cast iron with a burner? If so they can overshoot their own stat
quite a bit when that switches the boiler off so it won't run again
until it's cooled down.

As far as the burner is concerned what is the difference between the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case there
will be a "boiler on" input to control the actual fireing.

From what you say having the boiler properly controlled by the demand
will save you a fair bit of oil.

--
Cheers
Dave.

Martin Brown wrote:

I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

The model installed is a Heatmiser RC1-WTS rev 1.0
zone 1 = CH (room thermostat) and zone 2 = HW.

I have a heatmiser (PRT-HW-TS-WIFI but no difference) driving an old gas
fired cast iron lump, gravity H/W and pumped C/H, I had to use a relay
when wiring it so that when the H/W output of the heatmiser was on it
fired boiler only, and when the C/H output was on it fired boiler and
ran the pump, obviously couldn't just wire both outputs direct to the
boiler, or they'd both also be wired to the pump.

My boiler just has L/N/E connections to turn it on, no permanent live or
PCB required as it has a pilot light, I just set the boiler's internal
stat to maximum so it's never satisfied and therefore it fires whenever
the heatmiser asks for it (unless H/W only and the tank stat is satisfied).

On 19/03/2014 19:05, Dave Liquorice wrote:
As far as the burner is concerned what is the difference between the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case there
will be a "boiler on" input to control the actual fireing.

If it's like mine - the fuel pump goes off first, then the fan. And the
water pump is still running.

External control stops it dead.

I need to rewire it, so come summer we can have HW and not heating,
which is currently not possible.

Andy

On 19/03/2014 19:00, Martin Brown wrote:
On 19/03/2014 15:22, Roger Mills wrote:


By 'smart controller' do you mean a programmable room stat? What make
and model? The instructions are often a bit cryptic, but you can usually
fathom them if you read them a few times.

I mean one that calibrates itself to the thermal inertia of the house
and fires the boiler at the appropriate time(s) to hit the specified way
points on the temperature profile at its thermostat.

The model installed is a Heatmiser RC1-WTS rev 1.0
zone 1 = CH (room thermostat) and zone 2 = HW.

My Honeywell stat has an 'Optimum Start' function, where it can decide
when to start the heating to achieve the set point at a specific time -
based on the temperature difference and its assessment of the house
heat-up rate. I've disabled that because I found that the heating was
coming on ridiculously early. I now start it at a fixed time - and it
might not always be *quite* up to temperature when I get up, but it's
near enough and I'm using a *lot* less gas.

In your case, it's even more complicated. How is the controller supposed
to know whether or not the wood burner is running?


It functions but it seems to be abusing the boiler...

I don't know a lot about oil-fired boilers, but my Honeywell
programmable stat does have a mode with a longer minimum 'on' time for
use with oil boilers, but it still isn't *very* long. You must surely be
able to turn the boiler off when it's firing, when all demands are
satisfied? If not, there's little point in have a 'smart' control system!

You can but it doesn't shut down at all gracefully since it should
switch off properly with a purge of exhaust gasses rather than just
stopping dead as all mains is suddenly removed. It didn't seem to be a
bother it with the old once or twice a day basic controller but then a
fair proportion of the time it wouldn't be flame active when dropped off
power since it would happen at the end of an hour or so with the house
or hot water probably full satisfied and the boiler up to temperature
already in its standby state rather than active.

The new controller is pretty much forever switching the boiler off when
the flame is lit and the boiler isn't at all happy with it's lot.


I'm still at a bit of a loss to know what the difference is between
having the boiler's stat cut power to the burner on the one hand, or
having an external stat do it on the other.

Mention of the permanent live and switched live in an adjacent response
has given me something to look for, but I think this unit may be so old
as not to make the distinction.

If there *is* a difference - as per my previous paragraph - it must be
due to something like that. It sounds as if the boiler's internal stat
is cutting power to the burner whilst maintaining power to the fan and
to whatever does the purge. With the use of a permanent live and a
switched live you might be able to make your controller do the same
thing. You may find that there are two live inputs - currently strapped
together - and that you need to unstrap them and connect a permanent
live feed to one, and a switched live from your controller to the other.
--
Cheers,
Roger
____________
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checked.

On 19/03/2014 19:05, Dave Liquorice wrote:
On Wed, 19 Mar 2014 10:12:16 +0000, Martin Brown wrote:

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What do you mean by that? You say "old oil boiler" is it a gert lump
of cast iron with a burner? If so they can overshoot their own stat
quite a bit when that switches the boiler off so it won't run again
until it's cooled down.

Yes. It is exactly that. The great lump of cast iron is practically
indestructible and has outlived the original burner by some margin.

As far as the burner is concerned what is the difference between the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case there
will be a "boiler on" input to control the actual fireing.

There might be but that is definitely not how it has ever been wired. If
it shuts down on its own thermostat it does the right

The old timer system did sometimes go down with a crunch if the flame
happened to be lit when the timer suddenly switched it off. But the new
smart room thermostat is doing it almost every time with the burner
running and unburnt kerosene fumes result (noticeable inside and out).

From what you say having the boiler properly controlled by the demand
will save you a fair bit of oil.

That was what I thought too and the idea behind fitting one. And also
with it having a 5+2 world model a chance of a lie in at weekends.

So far it is probably going to destroy another burner jet with soot
before I get to the bottom of how it should have been wired up.

--
Regards,
Martin Brown

On Wed, 19 Mar 2014 21:04:37 +0000, Vir Campestris wrote:

As far as the burner is concerned what is the difference between
the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case
there
will be a "boiler on" input to control the actual fireing.

If it's like mine - the fuel pump goes off first, then the fan. And the
water pump is still running.

On mine there is only one motor that drives the fan and pump. Single
LNE in with the live series connected through the boiler stat and
hi-limit stat.

Mind you this is a big floor standing cast iron jobbie that holds 12
gallons of water not a tiddly little ali thing with almost no water
in it. B-)

--
Cheers
Dave.

On 19/03/2014 10:12, Martin Brown wrote:
I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

The old system was CH controlled only pump and HW controlled only boiler
which meant that the boiler was live most of the day (or twice daily)
with only one or two potentially brutal power offs mid-flame.

The new thermostatic control has the potential to do this sort of
unfriendly cut to the power feed several times a day. Apart from setting
minimum cycle time to 15 minutes is there anything else I can do? I
suppose it wouldn't bother a gas boiler so much.

Obvious fix being a relay to hold mains on until the boiler fan stops
drawing current (but that requires a modification to the boiler).

The advantages of smart start to match target temperature is largely
eliminated if I have to set the boiler to come on at some God forsaken
hour of the morning just in case the CH pump thinks it needs to be on.

Incidentally why don't these smart controllers provide decent manuals in
English with more sensible boiler and pump control outputs?


I have not had a problem with my Danfoss programmable thermostat
switching my pump and oil boiler off and on several times an hour.

The programmer is two channel. The second channel is used to heat hot
water twice per day. The manual is in English.


--
Michael Chare

On 19/03/2014 22:06, Dave Liquorice wrote:
On Wed, 19 Mar 2014 21:04:37 +0000, Vir Campestris wrote:

As far as the burner is concerned what is the difference between
the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case
there
will be a "boiler on" input to control the actual fireing.

If it's like mine - the fuel pump goes off first, then the fan. And the
water pump is still running.

On mine there is only one motor that drives the fan and pump. Single
LNE in with the live series connected through the boiler stat and
hi-limit stat.

Mind you this is a big floor standing cast iron jobbie that holds 12
gallons of water not a tiddly little ali thing with almost no water
in it. B-)


My more modern one is much the same. I can't see why youe would want a
fan over run. All it would do is blow cold air through the boiler to the
outside and remove some of the residual heat.

--
Michael Chare

On 19/03/2014 22:06, Dave Liquorice wrote:
On Wed, 19 Mar 2014 21:04:37 +0000, Vir Campestris wrote:

As far as the burner is concerned what is the difference between
the
boilers stat yanking the power or an external one? There might be
some form of over run for the pump and/or fan but in that case
there
will be a "boiler on" input to control the actual fireing.

There might be. I will have to take a detailed look at the weekend.
Our boiler like the master phone socket is conveniently located in the
loft (very close to the hot water tank which is a bonus I suppose).

If it's like mine - the fuel pump goes off first, then the fan. And the
water pump is still running.

On mine there is only one motor that drives the fan and pump. Single
LNE in with the live series connected through the boiler stat and
hi-limit stat.

Mine is like yours, but I think you will find there is a solenoid valve
that cuts the fuel supply off leaving just the fan running for about 5s
at the end of a controlled flame burn to tidy up and vent the flue.

It is lack of this action that seems to be the problem with mine.

Mind you this is a big floor standing cast iron jobbie that holds 12
gallons of water not a tiddly little ali thing with almost no water
in it. B-)

Mine is also brutal floor standing cast iron job and physically much
wider than the slimline 15/19 shown in the modern brochure. The scifi
computer writing on the front adds a touch of surrealism.

--
Regards,
Martin Brown

On Thu, 20 Mar 2014 09:33:17 +0000, Martin Brown wrote:

As far as the burner is concerned what is the difference between
the boilers stat yanking the power or an external one? There
might be
some form of over run for the pump and/or fan but in that case
there will be a "boiler on" input to control the actual fireing.

There might be. I will have to take a detailed look at the weekend.

If it's like mine - the fuel pump goes off first, then the fan.
And
the water pump is still running.

On mine there is only one motor that drives the fan and pump.
Single
LNE in with the live series connected through the boiler stat and
hi-limit stat.

Mine is like yours, but I think you will find there is a solenoid valve
that cuts the fuel supply off leaving just the fan running for about 5s
at the end of a controlled flame burn to tidy up and vent the flue.

If "like yours" is refering to my oil boiler with a single switched
LNE feed how does the fan run on for 5s after the oil solenoid has
closed as there is no power? It'll be spinning down but that isn't
the same as being driven. Yes my boiler does have an oil solenoid
valve but that'll close the same time as the fan is depowered.

It's main use is start up, power arrives, fan and pump runs, a few
seconds later the valve opens and the spark is started, if no flame
is detected within about 10 seconds it locks out.

--
Cheers
Dave.

On Thu, 20 Mar 2014 00:15:04 +0000, Michael Chare wrote:

My more modern one is much the same. I can't see why youe would want a
fan over run. All it would do is blow cold air through the boiler to the
outside and remove some of the residual heat.

Only to clear the flue gases, my boiler is a open flue one with a 5+
m 5" flue so has a hefty draw so clearing the gases isn't a problem.
For a smaller balanced flue boiler it might be but even then just a
few seconds will be enough.

--
Cheers
Dave.

On Wed, 19 Mar 2014 21:05:29 +0000, Roger Mills wrote:

In your case, it's even more complicated. How is the controller supposed
to know whether or not the wood burner is running?

It doesn't need to. The wood burner shows as reduced demand for heat,
ie the room stat won't call for heat as often or will be satisfied
earlier due to the extra heat supplied by wood burner.

It's not ideal, a thermal store to buffer the heat from all sources
would be better. With above there is the chance that the boiler may
only fire for a short time, a thermal store ensures that the boiler
will get a decent length burn as it heats the store from luke warm to
hot.

--
Cheers
Dave.

On 20/03/2014 10:29, Dave Liquorice wrote:
On Thu, 20 Mar 2014 09:33:17 +0000, Martin Brown wrote:


Mine is like yours, but I think you will find there is a solenoid valve
that cuts the fuel supply off leaving just the fan running for about 5s
at the end of a controlled flame burn to tidy up and vent the flue.

If "like yours" is refering to my oil boiler with a single switched
LNE feed how does the fan run on for 5s after the oil solenoid has
closed as there is no power? It'll be spinning down but that isn't
the same as being driven. Yes my boiler does have an oil solenoid
valve but that'll close the same time as the fan is depowered.

On mine there is a magic control box which has an LDR to detect flame is
good and timer to fire the ignition coil, the same timer on shutdown
also keeps the fan running after the thermostat signals at temperature.

ISTR There is a bunch of 3 DPCO 10A mains relays inside doing the actual
power switching based on what the control box tells them to do.

It's main use is start up, power arrives, fan and pump runs, a few
seconds later the valve opens and the spark is started, if no flame
is detected within about 10 seconds it locks out.

Pretty much the same here or start up.

But at end of flame it closes off the fuel solenoid and runs the fan for
about 5s to clear the balanced flue of combustion products. This
obviously doesn't happen if you just cut the mains feed off externally.

--
Regards,
Martin Brown

On 19/03/2014 13:36, dennis@home wrote:
On 19/03/2014 10:12, Martin Brown wrote:
I have just got a smart CH controller with room thermostat which will
probably be used to switch both the CH pump and an old oil boiler.

However, I notice that the boiler much prefers to run until its own
thermostat is satisfied and seems to be a bit recalcitrant if it is
switched on and off by external forces too often.

What is the accepted way around this?

Most boilers these days have a permanent live and a boiler on.
You need to check and use the boiler on not just switch the mains on and
off.

It is an old and robust oil boiler vintage circa 1970's.

I will take a look to see if there is any provision for boiler on vs
permanent live but I somehow doubt it.

--
Regards,
Martin Brown

On 20/03/2014 10:32, Dave Liquorice wrote:
On Thu, 20 Mar 2014 00:15:04 +0000, Michael Chare wrote:

My more modern one is much the same. I can't see why youe would want a
fan over run. All it would do is blow cold air through the boiler to the
outside and remove some of the residual heat.

Only to clear the flue gases, my boiler is a open flue one with a 5+
m 5" flue so has a hefty draw so clearing the gases isn't a problem.
For a smaller balanced flue boiler it might be but even then just a
few seconds will be enough.


It might help to prevent condensation in the flue.


--
Michael Chare

On Wednesday, March 19, 2014 9:05:29 PM UTC, Roger Mills wrote:

My Honeywell stat has an 'Optimum Start' function, where it can decide
when to start the heating to achieve the set point at a specific time -
based on the temperature difference and its assessment of the house heat-up
rate. I've disabled that because I found that the heating was coming on
ridiculously early. I now start it at a fixed time - and it might not always
be *quite* up to temperature when I get up, but it's near enough and I'm
using a *lot* less gas.

Be careful what conclusions your draw from that though.

I ran some experiments over several weeks with my CM927 and a time-lapse webcam automatic detecting calls for heat. I found that it was surprisingly accurate at reaching the target temperature (0.5C resolution) just on time - nearly always no sooner/later than 5-10 minutes. The environmental conditions were quite varied too and so it really got a good chance to exercise its adapting capability and highlight any weaknesses.

Given this accuracy I would have to put any potential gas savings obtained from disabling optimum start down to me accepting that the target temperature might not be reached on time or, to put it another way, that my target time could slip.

Mathew

On 20/03/2014 10:54, Dave Liquorice wrote:
On Wed, 19 Mar 2014 21:05:29 +0000, Roger Mills wrote:

In your case, it's even more complicated. How is the controller supposed
to know whether or not the wood burner is running?

It doesn't need to. The wood burner shows as reduced demand for heat,
ie the room stat won't call for heat as often or will be satisfied
earlier due to the extra heat supplied by wood burner.


I think you're slightly missing the point I was making. For normal
real-time control, what you say is true.

But I was talking about the optimum start function, where the stat
decides when to turn the heating on first thing in the morning, based on
what it has previously learned about the dynamics of the system. It
doesn't know whether you're going to light the wood burner part-way
through its warm-up cycle.
--
Cheers,
Roger
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checked.

On 20/03/2014 13:36, Mathew Newton wrote:
On Wednesday, March 19, 2014 9:05:29 PM UTC, Roger Mills wrote:

My Honeywell stat has an 'Optimum Start' function, where it can decide
when to start the heating to achieve the set point at a specific time -
based on the temperature difference and its assessment of the house heat-up
rate. I've disabled that because I found that the heating was coming on
ridiculously early. I now start it at a fixed time - and it might not always
be *quite* up to temperature when I get up, but it's near enough and I'm
using a *lot* less gas.

Be careful what conclusions your draw from that though.

I ran some experiments over several weeks with my CM927 and a time-lapse webcam automatic detecting calls for heat. I found that it was surprisingly accurate at reaching the target temperature (0.5C resolution) just on time - nearly always no sooner/later than 5-10 minutes. The environmental conditions were quite varied too and so it really got a good chance to exercise its adapting capability and highlight any weaknesses.

Given this accuracy I would have to put any potential gas savings obtained from disabling optimum start down to me accepting that the target temperature might not be reached on time or, to put it another way, that my target time could slip.

Mathew

Maybe mine wasn't working properly, but if I needed to go to the toilet
very early in the morning, the radiator in the bathroom would often be
hot - and I concluded that the stat was turning the boiler on a full 3
hours (the max time it uses) in advance which it certainly didn't need
to. I've now disabled optimum start and programmed the heating to come
on one hour before my alarm goes off - and that's always been enough,
even in very cold weather.
--
Cheers,
Roger
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