We used to have an old bimetallic Honeywell thermostat but it always seemed
wildly inaccurate and slow to switch on or off.

I thought my problems would be solved by going digital with one of these.

https://www.amazon.co.uk/dp/B07YPQRC...ZZEB6SY8BFE7VE

Today however, it was getting uncomfortably warm in our hall. The
thermostat was set to twenty, it was displaying 20.5 and was still calling
for heat ( flame symbol in display).

Shouldnt it have turned itself off at 20 or are digital ones designed to
keep calling for heat for a period after reaching the target temperature?

Tim

--
Please don't feed the trolls

Tim+ wrote:

The thermostat was set to twenty, it was displaying 20.5 and was
still calling for heat ( flame symbol in display).

Shouldnt it have turned itself off at 20

On mine can set the accuracy to 0.5, 1.0 or 2.0 degrees. Probably
depends if you've got a cast iron lump or a modulating boiler which you
should choose ...

On 04/05/2021 22:13, Tim+ wrote:

We used to have an old bimetallic Honeywell thermostat but it always seemed
wildly inaccurate and slow to switch on or off.

I thought my problems would be solved by going digital with one of these.

https://www.amazon.co.uk/dp/B07YPQRC...ZZEB6SY8BFE7VE

Today however, it was getting uncomfortably warm in our hall. The
thermostat was set to twenty, it was displaying 20.5 and was still calling
for heat ( flame symbol in display).

Shouldnt it have turned itself off at 20 or are digital ones designed to
keep calling for heat for a period after reaching the target temperature?

Tim


Cannot you use the buttons to manually adjust the target temperature to
find at which point the thermostat stops calling for heat? If its
anything like my thermostat the first press of the button will display
the actual target temperature, the second press will then reduce the
target by 1C. At this point leave it for say 30 seconds to see if call
for heat turns off. Repeat with lower temperatures if still calling for
heat.

Or, perhaps it is the function of the proportional bandwidth facility
(setting) on the thermostat that is attempting to modulate the firing of
an older boiler as the temperature reaches the target and the thermostat
tries to be clever to maintain that temperature that is causing the problem

The following thread may give some insight - read to the 9th post in

https://www.diynot.com/diy/threads/h...mostat.313953/






--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 05/05/2021 06:37, alan_m wrote:

The following thread may give some insight - read to the 9th post in

https://www.diynot.com/diy/threads/h...mostat.313953/


The discussion is about the wireless version of the thermostat so
different model number.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

alan_m wrote:
On 04/05/2021 22:13, Tim+ wrote:

We used to have an old bimetallic Honeywell thermostat but it always seemed
wildly inaccurate and slow to switch on or off.

I thought my problems would be solved by going digital with one of these.

https://www.amazon.co.uk/dp/B07YPQRC...ZZEB6SY8BFE7VE

Today however, it was getting uncomfortably warm in our hall. The
thermostat was set to twenty, it was displaying 20.5 and was still calling
for heat ( flame symbol in display).

Shouldnt it have turned itself off at 20 or are digital ones designed to
keep calling for heat for a period after reaching the target temperature?

Tim


Cannot you use the buttons to manually adjust the target temperature to
find at which point the thermostat stops calling for heat? If its
anything like my thermostat the first press of the button will display
the actual target temperature, the second press will then reduce the
target by 1C. At this point leave it for say 30 seconds to see if call
for heat turns off. Repeat with lower temperatures if still calling for
heat.

Or, perhaps it is the function of the proportional bandwidth facility
(setting) on the thermostat that is attempting to modulate the firing of
an older boiler as the temperature reaches the target and the thermostat
tries to be clever to maintain that temperature that is causing the problem

The following thread may give some insight - read to the 9th post in

https://www.diynot.com/diy/threads/h...mostat.313953/


Thanks, that was very helpful. Its probably just operating as designed
then. Ive dug out the instructions and see that it is possible adjust the
proportional band width. I might have a fiddle. ;-)

Tim

--
Please don't feed the trolls

alan_m wrote:
On 05/05/2021 06:37, alan_m wrote:

The following thread may give some insight - read to the 9th post in

https://www.diynot.com/diy/threads/h...mostat.313953/


The discussion is about the wireless version of the thermostat so
different model number.


The principle of proportional bandwidth is the same though so still useful.

Tim

--
Please don't feed the trolls

Tim+ formulated the question :
Shouldnt it have turned itself off at 20 or are digital ones designed to
keep calling for heat for a period after reaching the target temperature?

Digital ones also have to have hysteresis too, otherwise your heating
system would be switching on and off too rapidly.

There are better ways - You can buy integrated systems which are able
to predict how much heat input is needed, so as to just hit the set
temperature, then as that is neared, they ramp the boiler output down
and eventually off. When more heat input is needed, they will run the
boiler at a suitably low output, that they don't over shoot the
setting.

I have such a system and it makes the heating system unoticeable, no
more temperature cycling as the boiler cuts in and out, no noise as
pipes expand and contract.

On 04/05/2021 22:13, Tim+ wrote:

Today however, it was getting uncomfortably warm in our hall. The
thermostat was set to twenty, it was displaying 20.5 and was still calling
for heat ( flame symbol in display).


I bought three wall heaters for work a few years ago, rather than the 10
quid plastic ones we'd normally dot around when it's brass monkeys I
spent good money on some 'nice' glass panel digital ones.

They had a 5 degree gap between calling for heat and not. Set them at 21
they'd come on at 18.5 and go off at 23.5 so rarely a comfortable heat.

The timer on them was like a Japanese riddle, you (or I at least) could
only set it by way of a fluke.

But it's OK because all 3 packed in and we're back to the pound job jobbies.

On 04/05/2021 22:13, Tim+ wrote:


Today however, it was getting uncomfortably warm in our hall.

I should add to my prior post, everyone I live/work with* has no respect
for a thermostat and will ramp them up to max in the bizarre hope that
they will heat an area up more quickly.


*And share a car with.

"R D S" wrote in message
...
On 04/05/2021 22:13, Tim+ wrote:


Today however, it was getting uncomfortably warm in our hall.

I should add to my prior post, everyone I live/work with* has no respect
for a thermostat and will ramp them up to max in the bizarre hope that
they will heat an area up more quickly.

Anyone who has had a gas oven will be familiar with the concept of a high
gas mark (temperature) giving a higher power (gas flow) than a low one. In
other words, from cold, gas mark 9 followed by gas mark 4 when it's up to
temp will result in the oven getting up to the final temperature of gas mark
4 quicker than gas mark 4 from the start: a gas "regulo" controls both power
and on/off cycling temperature. I presume once the oven is at temp, it
alternates between virtually off (just enough to keep the burner alight) and
full, in a similar way to an electric oven, but when it's heating up from
cold, the rate of heating is controlled by the gas mark setting. I presume
that's still the case; we've always had an electric oven, but my parents
have gas and I'm basing my comments on how their oven behaved.


When we changed our previous house and our present house from (in each case)
a conventional thermostat to Hive, we noticed that the temperatures remained
a lot more constant. I think originally the temperature stayed within about
+/- 3 degC of the required value, whereas it's now within about +/- 0.5 degC
(*). That's ignoring any additional temperature rise due to the sun (the
room where the thermostat lives is south-facing) which sometimes causes a
temperature rise that outweighs the fact that the central heating then
doesn't come on as much.

I imagine that solid-state temperature sensors have no hysteresis at all,
and the control circuit has to have a defined amount of hysteresis built in
to avoid the boiler turning on/off too frequently.


(*) Looking at today's figures, the temperature on the Hive is set to change
from 17 (overnight) to 21.5 (from 0800). The actual temperature overnight
dropped gradually to a low of 18.5 at 0630, then rose to reach a steady
state of around 21 by 1000, and from then until now it's varied from 21.1 to
21.9. With Hive, you don't have the boiler timed to go off overnight, you
simply set a lower desired temperature overnight which means it usually
never comes on (because actual desired) but occasionally comes on if it's
a cold night and the actual drops below the desired.

NY wrote:
"R D S" wrote in message
...
On 04/05/2021 22:13, Tim+ wrote:


Today however, it was getting uncomfortably warm in our hall.

I should add to my prior post, everyone I live/work with* has no respect
for a thermostat and will ramp them up to max in the bizarre hope that
they will heat an area up more quickly.

Anyone who has had a gas oven will be familiar with the concept of a high
gas mark (temperature) giving a higher power (gas flow) than a low one. In
other words, from cold, gas mark 9 followed by gas mark 4 when it's up to
temp will result in the oven getting up to the final temperature of gas mark
4 quicker than gas mark 4 from the start:

Nope. Im almost certain that our old gas oven gave a €œfull size€� flame
from cold whatever the temperature setting. The temperature control just
changed the temperature at which the flame modulates down.

a gas "regulo" controls both power
and on/off cycling temperature. I presume once the oven is at temp, it
alternates between virtually off (just enough to keep the burner alight) and
full, in a similar way to an electric oven, but when it's heating up from
cold, the rate of heating is controlled by the gas mark setting. I presume
that's still the case; we've always had an electric oven, but my parents
have gas and I'm basing my comments on how their oven behaved.

How it behaved or how they €œbelieved€� it behaved? The idea that turning a
stat up to full will speed up the rate of heating with any sort of heating
system is so pervasive Im sure many folk believe it absolutely.

Tim

--
Please don't feed the trolls

On 05/05/2021 18:27, NY wrote:
Anyone who has had a gas oven will be familiar with the concept of a
high gas mark (temperature) giving a higher power (gas flow) than a low
one. In other words, from cold, gas mark 9 followed by gas mark 4 when
it's up to temp will result in the oven getting up to the final
temperature of gas mark 4 quicker than gas mark 4 from the start: a gas
"regulo" controls both power and on/off cycling temperature. I presume
once the oven is at temp, it alternates between virtually off (just
enough to keep the burner alight) and full, in a similar way to an
electric oven, but when it's heating up from cold, the rate of heating
is controlled by the gas mark setting. I presume that's still the case;
we've always had an electric oven, but my parents have gas and I'm
basing my comments on how their oven behaved.

No oven I have ever encountered behaved like that


--
"Strange as it seems, no amount of learning can cure stupidity, and
higher education positively fortifies it."

- Stephen Vizinczey

On 05/05/2021 19:02, Tim+ wrote:
How it behaved or how they €œbelieved€� it behaved? The idea that turning a
stat up to full will speed up the rate of heating with any sort of heating
system is so pervasive Im sure many folk believe it absolutely.

that is because that is the way every non thermostatically regulated
system behaves.

And the world is full of ArtStudents„¢



--
€œSome people like to travel by train because it combines the slowness of
a car with the cramped public exposure of €¨an airplane.€�

Dennis Miller

On 04/05/2021 22:13, Tim+ wrote:

I thought my problems would be solved by going digital with one of these.

https://www.amazon.co.uk/dp/B07YPQRC...ZZEB6SY8BFE7VE

Today however, it was getting uncomfortably warm in our hall. The
thermostat was set to twenty, it was displaying 20.5 and was still calling
for heat ( flame symbol in display).

Shouldnt it have turned itself off at 20 or are digital ones designed to
keep calling for heat for a period after reaching the target temperature?

From the manufacturer's blurb it looks like it uses electronic
proportional control logic instead of relying on a physical hysteresis.
As the temperature approaches the set point it modulates the heat supply
by progressively reducing the duty cycle in order to avoid overshooting
the target. The call for heat indicator doesn't necessarily mean that
the heater or boiler is actually running because the indicator remains
on during both the 'on' and 'off' parts of the duty cycle.

Even at the set point, or even slightly above this, its indicator still
shows a call for heat because a low level of heat input is still needed
to balance heat losses. Our Honeywell CM927 works this way maintaining
the temperature within +/- 0.5 deg C of the set point, and it does still
show a call for heat when 0.5 deg above.

Incidentally with this type of thermostat the theory of temporarily
turning it up to a higher value can in some cases actually result in
heating the house slightly quicker because you don't get the reduced
duty cycle during the last few degrees as you approach the temperature
you want.

"The Natural Philosopher" wrote in message
...
On 05/05/2021 18:27, NY wrote:
Anyone who has had a gas oven will be familiar with the concept of a high
gas mark (temperature) giving a higher power (gas flow) than a low one.
In other words, from cold, gas mark 9 followed by gas mark 4 when it's up
to temp will result in the oven getting up to the final temperature of
gas mark 4 quicker than gas mark 4 from the start: a gas "regulo"
controls both power and on/off cycling temperature. I presume once the
oven is at temp, it alternates between virtually off (just enough to keep
the burner alight) and full, in a similar way to an electric oven, but
when it's heating up from cold, the rate of heating is controlled by the
gas mark setting. I presume that's still the case; we've always had an
electric oven, but my parents have gas and I'm basing my comments on how
their oven behaved.

No oven I have ever encountered behaved like that

Maybe my parents' oven was unusual then, and I've extrapolated to thinking
this was how *all* gas ovens behaved. Sorry, if that's the case.

I know that if you lit it (by putting a taper down the lighting hole at the
front of the bottom of the oven), the size of the flame in the burners
varied according to how far round the "regulo" knob was turned. There was no
"full on or barely lit" with no gradation in between. Once it got up to
temperature, *then* there was a sharp change from barely on to full on at
around the temperature it was set to, but when it was cold there was a full
range of flame heights, so starting it on maximum temperature *did* actually
make it heat up quicker - unlike every other appliance which is simply on or
off, so it would make no difference.

This was an oven that dated from 1962 (it was a wedding present to my
parents) and it lasted until the mid 90s when they called out a gas engineer
for some trivial fault and he condemned it as unsafe, so they had to have
fish and chips that night and go looking for a new cooker the following day,
living on microwave meals (no oven, hob or grill) until the new one was
delivered and fitted.

I remember that it originally had a "gas taper" for lighting the oven: this
was a thin flexible hose with a metal burner on the end, which you lit from
the main pilot light (no piezo lighting!) or from a gas hob burner, and then
transferred the little flame to the lighting hole in the oven. That hose got
trapped so many times in the oven door as it hung down on the hinge side of
the door when it was not in use, so it was removed and blanked-off when the
Gas Board were converting everyone's cookers from coal gas to natural gas.

The Natural Philosopher has brought this to us :
No oven I have ever encountered behaved like that

Likewise and obvious if you turn the control's setting. Set it to a mid
setting, watch the flame and when it hits that setting the flame
significantly reduces to a low level. Turn it up a notch, the flame
goes to maximum. Turn it down the flame reduces to minimum, until the
cools down to the new setting. All done by capillary tube and expansion
inside the tube, controlling the jet's supply of gas.