I have a Honeywell CM67 on my central heating and I have noticed that it is
calling for heat several times an hour even though it states that it is at
the correct temperature. When it is at the correct temp it only calls for
heat for a minute or two. This seems a real waste. I noticed on the
installer menu that there are 2 settings which may affect this. The first
is the cycle rate and the default is 6, which is about as often as the
thermostat is calling for heat when it doesn't appear to need so. Could
this be why? If it is, can this be set to 3 ( this seems to be the lowest)
to reduce the times or does it need to be 6? Also there is a minimum ON
time which is set to 1 minute as a default and this can be set from 1 to 5
minutes. Does that make a difference?

Advice is appreciated.

Angela

On Oct 18, 3:51*pm, "Angela" wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it is
calling for heat several times an hour even though it states that it is at
the correct temperature. *When it is at the correct temp it only calls for
heat for a minute or two. *This seems a real waste. *I noticed on the
installer menu that there are 2 settings which may affect this. *The first
is the cycle rate and the default is 6, which is about as often as the
thermostat is calling for heat when it doesn't appear to need so. *Could
this be why? *If it is, can this be set to 3 ( this seems to be the lowest)
to reduce the times or does it need to be 6? *Also there is a minimum ON
time which is set to 1 minute as a default and this can be set from 1 to 5
minutes. *Does that make a difference?

Advice is appreciated.

Angela

Heating systems run more efficently the longer the cycle and wider the
swing in temp, short cycling as you are doing is wearing out all
components that switch on, since only so many cycles are built in to
any equipment. The first maybe 5 minutes any small heating system is
on is the most inefficent, it has to warm up, try both at max swing
and temp run time and see what happens, if temp swings to much for
comfort reduce it until you are happy

"ransley" wrote in message
...
On Oct 18, 3:51 pm, "Angela" wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it
is
calling for heat several times an hour even though it states that it is at
the correct temperature. When it is at the correct temp it only calls for
heat for a minute or two. This seems a real waste. I noticed on the
installer menu that there are 2 settings which may affect this. The first
is the cycle rate and the default is 6, which is about as often as the
thermostat is calling for heat when it doesn't appear to need so. Could
this be why? If it is, can this be set to 3 ( this seems to be the lowest)
to reduce the times or does it need to be 6? Also there is a minimum ON
time which is set to 1 minute as a default and this can be set from 1 to 5
minutes. Does that make a difference?

Advice is appreciated.

Angela

Heating systems run more efficently the longer the cycle and wider the
swing in temp, short cycling as you are doing is wearing out all
components that switch on, since only so many cycles are built in to
any equipment. The first maybe 5 minutes any small heating system is
on is the most inefficent, it has to warm up, try both at max swing
and temp run time and see what happens, if temp swings to much for
comfort reduce it until you are happy

Sorry, can I just clarify that have I have understood, I should reduce the
cycle rate to 3 and the min time on to max (5 minutes)?

Angela

Angela wrote:

I have a Honeywell CM67 on my central heating and I have noticed that it
is calling for heat several times an hour even though it states that it is
at the correct temperature. *When it is at the correct temp it only calls
for heat for a minute or two.

Yes, that's normal.

This seems a real waste.

Not really. When you heat your house up to your desired temperature it
looses heat to the outside world. With a "conventional" thermostat there is
some hysteresis which causes it to switch off until the temperature drops
sufficiently for it to cut in again, resulting in an erratic temperature.
The programmer uses some clever logic to provide enough heat to balance the
heat losses to the outside and maintain a much more steady temperature. It
does this by varying the length of time to fire the boiler every ten
minutes. When it's not very cold outside and you've arrived at the target
temperature the heating periods are quite short but get longer as the
weather gets colder.

Our CM927 behaves in a similar way and keeps the temperature at a steady
value within half a degree of the target.

--
Mike Clarke

On 18 Oct, 21:51, "Angela" wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it is
calling for heat several times an hour even though it states that it is at
the correct temperature. *When it is at the correct temp it only calls for
heat for a minute or two. *This seems a real waste.

Hi Angela,

The late Mr Hall wrote an excellent post on this some years ago which
will explain in detail what's happening and why:

http://groups.google.co.uk/group/uk....ced42?hl=en-GB

You could try cutting the cycle rate down to 3 as there may well be
benefits as far as boiler life is concerned although do keep an eye on
how accurate the temperature is then maintained.

Mathew

*I noticed on the
installer menu that there are 2 settings which may affect this. *The first
is the cycle rate and the default is 6, which is about as often as the
thermostat is calling for heat when it doesn't appear to need so. *Could
this be why? *If it is, can this be set to 3 ( this seems to be the lowest)
to reduce the times or does it need to be 6? *Also there is a minimum ON
time which is set to 1 minute as a default and this can be set from 1 to 5
minutes. *Does that make a difference?

Advice is appreciated.

Angela

On Oct 18, 5:01*pm, Mike Clarke wrote:
Angela wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it
is calling for heat several times an hour even though it states that it is
at the correct temperature. *When it is at the correct temp it only calls
for heat for a minute or two.

Yes, that's normal.

This seems a real waste.

Not really. When you heat your house up to your desired temperature it
looses heat to the outside world. With a "conventional" thermostat there is
some hysteresis which causes it to switch off until the temperature drops
sufficiently for it to cut in again, resulting in an erratic temperature.
The programmer uses some clever logic to provide enough heat to balance the
heat losses to the outside and maintain a much more steady temperature. It
does this by varying the length of time to fire the boiler every ten
minutes. When it's not very cold outside and you've arrived at the target
temperature the heating periods are quite short but get longer as the
weather gets colder.

Our CM927 behaves in a similar way and keeps the temperature at a steady
value within half a degree of the target.

--
Mike Clarke

Cycling 6x an hour, 144x a day is a waste in efficency and equipment
life, If this is a radiator HW set up its unbelievable, I cycle at 50f
outside maybe 8x a day. Your wear and tear on equipment is startup,
just look at surge load for motors.

Angela wrote:
"ransley" wrote in message
...
On Oct 18, 3:51 pm, "Angela" wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it
is
calling for heat several times an hour even though it states that it is at
the correct temperature. When it is at the correct temp it only calls for
heat for a minute or two. This seems a real waste. I noticed on the
installer menu that there are 2 settings which may affect this. The first
is the cycle rate and the default is 6, which is about as often as the
thermostat is calling for heat when it doesn't appear to need so. Could
this be why? If it is, can this be set to 3 ( this seems to be the lowest)
to reduce the times or does it need to be 6? Also there is a minimum ON
time which is set to 1 minute as a default and this can be set from 1 to 5
minutes. Does that make a difference?

Advice is appreciated.

Angela

Heating systems run more efficently the longer the cycle and wider the
swing in temp, short cycling as you are doing is wearing out all
components that switch on, since only so many cycles are built in to
any equipment. The first maybe 5 minutes any small heating system is
on is the most inefficent, it has to warm up, try both at max swing
and temp run time and see what happens, if temp swings to much for
comfort reduce it until you are happy

Sorry, can I just clarify that have I have understood, I should reduce the
cycle rate to 3 and the min time on to max (5 minutes)?

If you read Andy's post that Matthew linked to you should get a feeling
for what the stat is doing.

Personally, I would not be too worried about having the stat call for
heat six times / hour. Most stats will call for heat at least that often
unless the house is very well insulated, or the amount of temperature
swing permitted is rather large.

The default settings of the stat should work well enough on many systems
(and the stat will "learn" the typical operational performance of your
system and adapt its control to allow for the observed behaviour).

You may be able to tune for better operation if you are aware of
particular factors that affect your system. For example, if your boiler
is an older high water content type with a cast iron heat exchanger, you
may want to increase the minimum burn time a little since it will take a
while to get all that thermal mass up to temperature.

Optimising stats are good at getting accurate temperature and time
control out of relatively crude heating systems. However they are
sometimes less beneficial when used with boilers that already include
sophisticated control systems, since you can end up with unexpected
interactions between them.

Modern lightweight condensing modulating boilers may for example work
well with fewer cycles per hour since they will implement their own
closed loop control system to modulate the flow temperature of the water
in response to the actual heating load. Under light loads (i.e. return
water coming back at a highish temperature), these boilers will reduce
the flow temperature (promoting increased condensing efficiency), which
should allow longer burns at low power. However experimentation would be
required to select the optimal settings.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"ransley" wrote in message
...
On Oct 18, 5:01 pm, Mike Clarke wrote:
Angela wrote:
I have a Honeywell CM67 on my central heating and I have noticed that
it
is calling for heat several times an hour even though it states that it
is
at the correct temperature. When it is at the correct temp it only
calls
for heat for a minute or two.

Yes, that's normal.

This seems a real waste.

Not really. When you heat your house up to your desired temperature it
looses heat to the outside world. With a "conventional" thermostat there
is
some hysteresis which causes it to switch off until the temperature drops
sufficiently for it to cut in again, resulting in an erratic temperature.
The programmer uses some clever logic to provide enough heat to balance
the
heat losses to the outside and maintain a much more steady temperature.
It
does this by varying the length of time to fire the boiler every ten
minutes. When it's not very cold outside and you've arrived at the target
temperature the heating periods are quite short but get longer as the
weather gets colder.

Our CM927 behaves in a similar way and keeps the temperature at a steady
value within half a degree of the target.

--
Mike Clarke

Cycling 6x an hour, 144x a day is a waste in efficency and equipment
life, If this is a radiator HW set up its unbelievable, I cycle at 50f
outside maybe 8x a day. Your wear and tear on equipment is startup,
just look at surge load for motors.

Not withstanding the fact that a combination boiler seems to turn itself on
and off everytime some runs a hot water tap to rinse their hands!
Michael

"Mathew Newton" wrote in message
...
On 18 Oct, 21:51, "Angela" wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it
is
calling for heat several times an hour even though it states that it is
at
the correct temperature. When it is at the correct temp it only calls for
heat for a minute or two. This seems a real waste.

Hi Angela,

The late Mr Hall wrote an excellent post on this some years ago which
will explain in detail what's happening and why:

http://groups.google.co.uk/group/uk....ced42?hl=en-GB

You could try cutting the cycle rate down to 3 as there may well be
benefits as far as boiler life is concerned although do keep an eye on
how accurate the temperature is then maintained.

Mathew

That was a very useful post thank you Matthew. I "think" I now understand
what is happening. This is a new house with a new boiler but I notice that
the CM67 isn't sold any more - the developers/installers must have had a job
lot to get rid of. It seems fine though. I have only just started putting
the central heating on proper and it would appear that this thermostat can
"learn" and I probably haven't given it time to do that. I'll leave it at
the defaults for now and see how things go I think.

Angela

In an earlier contribution to this discussion,
Angela wrote:


That was a very useful post thank you Matthew. I "think" I now
understand what is happening. This is a new house with a new boiler
but I notice that the CM67 isn't sold any more - the
developers/installers must have had a job lot to get rid of. It
seems fine though. I have only just started putting the central
heating on proper and it would appear that this thermostat can
"learn" and I probably haven't given it time to do that. I'll leave
it at the defaults for now and see how things go I think.

Angela

Yes, you won't get a better explanation than that provided by Andy Hall.

As a matter of interest, does your CM67 have Optimum Start and, if so, is it
turned on?

[In case you're not familiar with it, Optimum Start is a feature whereby you
specify the time by which the house should be warm rather than the time at
which the heating should be switched on. The CM67 then decides when to
switch on, so it does it later in mild weather and earlier in cold weather -
helping to conserve fuel. It does this by 'learning' the rate of temperature
rise when the heating is on, so - depending on the starting temperature - it
knows how long it will take to get up to the required temperature. I have it
on mine, and I *think* it's a good thing - but it does sometimes seem to
turn the heating on *very* early in cold weather.]
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

"Roger Mills" wrote in message
...
| In an earlier contribution to this discussion,
| Angela wrote:
|
|
| That was a very useful post thank you Matthew. I "think" I now
| understand what is happening. This is a new house with a new boiler
| but I notice that the CM67 isn't sold any more - the
| developers/installers must have had a job lot to get rid of. It
| seems fine though. I have only just started putting the central
| heating on proper and it would appear that this thermostat can
| "learn" and I probably haven't given it time to do that. I'll leave
| it at the defaults for now and see how things go I think.
|
| Angela
|
| Yes, you won't get a better explanation than that provided by Andy Hall.
|
| As a matter of interest, does your CM67 have Optimum Start and, if so, is
it
| turned on?
|
| [In case you're not familiar with it, Optimum Start is a feature whereby
you
| specify the time by which the house should be warm rather than the time at
| which the heating should be switched on. The CM67 then decides when to
| switch on, so it does it later in mild weather and earlier in cold
weather -
| helping to conserve fuel. It does this by 'learning' the rate of
temperature
| rise when the heating is on, so - depending on the starting temperature -
it
| knows how long it will take to get up to the required temperature. I have
it
| on mine, and I *think* it's a good thing - but it does sometimes seem to
| turn the heating on *very* early in cold weather.]
| --
| Cheers,
| Roger

Yes it does have optimum start which will explian why it was on when I got
up this morning but according to the timer it wasn't due for another 5
minutes. I'll keep an eye on timing to see if it is turning on too early!

Angela wrote:

Yes it does have optimum start which will explian why it was on when I got
up this morning but according to the timer it wasn't due for another 5
minutes. I'll keep an eye on timing to see if it is turning on too early!

Once it has learnt the characteristics of the house, then it ought to
turn on just early enough ;-)

(so that if you say 20 degrees at 7am, that is the temperature it will
*be* at 7am rather than that being the target the system will start
aiming for at 7am)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
et...
| Angela wrote:
|
| Yes it does have optimum start which will explian why it was on when I
got
| up this morning but according to the timer it wasn't due for another 5
| minutes. I'll keep an eye on timing to see if it is turning on too
early!
|
| Once it has learnt the characteristics of the house, then it ought to
| turn on just early enough ;-)
|
| (so that if you say 20 degrees at 7am, that is the temperature it will
| *be* at 7am rather than that being the target the system will start
| aiming for at 7am)
|
| --
| Cheers,
|
| John.


Sounds perfect - lets see if it is!

On Sun, 19 Oct 2008 12:03:41 +0100 someone who may be "Roger Mills"
wrote this:-

[Optimum Start]

I *think* it's a good thing - but it does sometimes seem to
turn the heating on *very* early in cold weather.]

Has been used for more than two decades in large systems. Generally
a very good thing, but one flaw with it is that if the fabric of the
building becomes worse (open window for example) it will just learn
to start earlier (without optimum start someone may investigate why
the building is cold).

Optimum off is also a useful feature.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54