The recent very cold weather has thrown up a problem I hadn't noticed until
now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more than
enough to heat the house through about 20kW rated radiators.

And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then turning
off until the pump circulates the water enough for it to drop to the turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about 65
degC plus or minus a degree or two.

Have tried the pump (Grundfos Alpha) in every position on it and all give
the same effect, though some vary the time taken that the boiler spends on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

Whereas in warmer weather I didn't really notice the radiators warming up
and cooling so much now it is obvious that they are continually heating up
and cooling down with the boiler.


Arrangement is


|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |

|--------------------------------------------------------|----------|---|--
-|

Only unusual thing is the length of pipe between the boiler and pump - about
40 metres due to position of boiler in an outbuilding. Obviously it's 40m
back as well.
But temperature drop across this very well lagged pipe appears to be a
degree at most.

My guess is the pump doesn't circulate enough water and was thinking of
putting another pump in the return :

40m
|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |
|------------------------
ump ------------------------|----------|---|---|
40m

Should this help ?

Any alternative suggestions or routes to investigate gratefully received.

Many thanks

Mike

On Wed, 29 Dec 2004 20:16:35 -0000, "Mike" wrote:

The recent very cold weather has thrown up a problem I hadn't noticed until
now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more than
enough to heat the house through about 20kW rated radiators.

And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then turning
off until the pump circulates the water enough for it to drop to the turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about 65
degC plus or minus a degree or two.

Have tried the pump (Grundfos Alpha) in every position on it and all give
the same effect, though some vary the time taken that the boiler spends on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

Whereas in warmer weather I didn't really notice the radiators warming up
and cooling so much now it is obvious that they are continually heating up
and cooling down with the boiler.


Arrangement is


|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |

|--------------------------------------------------------|----------|---|--
-|

Only unusual thing is the length of pipe between the boiler and pump - about
40 metres due to position of boiler in an outbuilding. Obviously it's 40m
back as well.
But temperature drop across this very well lagged pipe appears to be a
degree at most.

My guess is the pump doesn't circulate enough water and was thinking of
putting another pump in the return :

40m
|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |
|------------------------
ump ------------------------|----------|---|---|
40m

Should this help ?

Any alternative suggestions or routes to investigate gratefully received.

Many thanks

Mike


Basically the flow rate is too low, as is the return temperature. You
have about 25 degrees temperature drop on a design that should be
about 12 degrees.

You don't say what pipe size your main 40m runs are, or which model
Alpha. Is it the larger one?

One relatively simple thing that you could try is to go and check all
the radiator lockshield valves and open them. If they are closed
down too low then this will restrict flow. Of course it may be that
some have to be quite a bit for balancing, but at least if you could
improve the flow it would help.

Beyond that, you could look through the design guide published by the
Copper Development Association and do the calculations for the pipe
runs.

http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf

If you plug in the numbers for the main pipe runs, that should give
some clue if there is something inadequate.

You can then work back and see if putting in a more powerful pump will
help (assuming that radiator tweaks don't)

--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Wed, 29 Dec 2004 20:16:35 -0000, "Mike" wrote:

The recent very cold weather has thrown up a problem I hadn't noticed
until
now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more
than
enough to heat the house through about 20kW rated radiators.

And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about
65
degC plus or minus a degree or two.

Have tried the pump (Grundfos Alpha) in every position on it and all give
the same effect, though some vary the time taken that the boiler spends
on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

Whereas in warmer weather I didn't really notice the radiators warming up
and cooling so much now it is obvious that they are continually heating
up
and cooling down with the boiler.


Arrangement is


|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |


|--------------------------------------------------------|----------|---|-
-
-|

Only unusual thing is the length of pipe between the boiler and pump -
about
40 metres due to position of boiler in an outbuilding. Obviously it's
40m
back as well.
But temperature drop across this very well lagged pipe appears to be a
degree at most.

My guess is the pump doesn't circulate enough water and was thinking of
putting another pump in the return :

40m
|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |
|------------------------
ump ------------------------|----------|---|---|
40m

Should this help ?

Any alternative suggestions or routes to investigate gratefully received.

Many thanks

Mike


Basically the flow rate is too low, as is the return temperature. You
have about 25 degrees temperature drop on a design that should be
about 12 degrees.

You don't say what pipe size your main 40m runs are,

Partially 28mm, but about 15m of flexible 22mm plastic was needed to poke
under a floor we couldn't get under properly. Did wonder at the time if I
might need to put in parallel runs of this pipe so there is a rope left to
allow more to be dragged through. However couldn't see a way of
parallelling these up without causing more resistance. Need a sort of Y
joint whereas all I could find were Ts or swept Ts.

or which model Alpha. Is it the larger one?

Yes



One relatively simple thing that you could try is to go and check all
the radiator lockshield valves and open them. If they are closed
down too low then this will restrict flow. Of course it may be that
some have to be quite a bit for balancing, but at least if you could
improve the flow it would help.

Two are flat out, rest are balanced to maintain all radiators at roughly the
same temperature drop.


Beyond that, you could look through the design guide published by the
Copper Development Association and do the calculations for the pipe
runs.

http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf

If you plug in the numbers for the main pipe runs, that should give
some clue if there is something inadequate.

Thanks - will do. Sounds to be what I need.



You can then work back and see if putting in a more powerful pump will
help (assuming that radiator tweaks don't)

--

.andy

To email, substitute .nospam with .gl

On Wed, 29 Dec 2004 20:58:19 -0000, "Mike" wrote:


"Andy Hall" wrote in message
.. .
On Wed, 29 Dec 2004 20:16:35 -0000, "Mike" wrote:



Basically the flow rate is too low, as is the return temperature. You
have about 25 degrees temperature drop on a design that should be
about 12 degrees.

You don't say what pipe size your main 40m runs are,

Partially 28mm, but about 15m of flexible 22mm plastic was needed to poke
under a floor we couldn't get under properly. Did wonder at the time if I
might need to put in parallel runs of this pipe so there is a rope left to
allow more to be dragged through. However couldn't see a way of
parallelling these up without causing more resistance. Need a sort of Y
joint whereas all I could find were Ts or swept Ts.

You'd have to compare the resistance of adding the fittings vs. having
the extra pipe. Also, for the plastic section, you may need to ask
the manufacturer because characteristics may well be different to
copper.



or which model Alpha. Is it the larger one?

Yes



One relatively simple thing that you could try is to go and check all
the radiator lockshield valves and open them. If they are closed
down too low then this will restrict flow. Of course it may be that
some have to be quite a bit for balancing, but at least if you could
improve the flow it would help.

Two are flat out, rest are balanced to maintain all radiators at roughly the
same temperature drop.


If the others are closed almost down in an effort to get a reasonable
temperature drop across these two, it sould indicate inadequate
pipework for the size/distance of them.

You could look up the radiator manufacturer data for the radiators (or
ones close to them). There is not an enormous difference between
vendors for typical finned radiators. THe main effect is the number
of panels and which have fins. If you find something close in size,
you can scale it. This should give you a gross heat output assuming
the EN testing method. You then need to look at the derating table
for the mean water to air temperature correction factor. For 82
degree flow and 70 return, (MWTA about 55 degrees) the normal derating
is to multiply by 0.9. So if you determine by size that a radiator
has a nominal output of 1kW, its actual output under what should be
the design conditions for your system will be 900W. You can then
take that figure and plug it into the CDA method and just check that
the pipework to those two radiators is adequate for them. A rough
rule of thumb is that 15mm pipe should be good to carry 6kW over
distances of a few metres (but not 40 :-) ).

You could try opening up a few of the other radiators (note the
lockshield positions for setting back) and see if it makes much
difference to the flow and return temperature on the main return. If
it does then probably the focus should be inside the house. If not,
then probably the long pipe runs and you could need a more powerful
pump.


Beyond that, you could look through the design guide published by the
Copper Development Association and do the calculations for the pipe
runs.

http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf

If you plug in the numbers for the main pipe runs, that should give
some clue if there is something inadequate.

Thanks - will do. Sounds to be what I need.

It's slightly laborious but you don't have to be hugely accurate.

In effect, the system is adrift by a factor of 2:1, so it should be
possible to deduce what is going wrong. You can work back to
determine the pump requirement given the resistance and from that see
if it is within the range of the pump.




You can then work back and see if putting in a more powerful pump will
help (assuming that radiator tweaks don't)

--

.andy

To email, substitute .nospam with .gl



--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Wed, 29 Dec 2004 20:58:19 -0000, "Mike" wrote:
Basically the flow rate is too low, as is the return temperature. You
have about 25 degrees temperature drop on a design that should be
about 12 degrees.

You don't say what pipe size your main 40m runs are,

Partially 28mm, but about 15m of flexible 22mm plastic was needed to poke
under a floor we couldn't get under properly. Did wonder at the time if
I
might need to put in parallel runs of this pipe so there is a rope left
to
allow more to be dragged through. However couldn't see a way of
parallelling these up without causing more resistance. Need a sort of Y
joint whereas all I could find were Ts or swept Ts.

You'd have to compare the resistance of adding the fittings vs. having
the extra pipe. Also, for the plastic section, you may need to ask
the manufacturer because characteristics may well be different to
copper.


One relatively simple thing that you could try is to go and check all
the radiator lockshield valves and open them. If they are closed
down too low then this will restrict flow. Of course it may be that
some have to be quite a bit for balancing, but at least if you could
improve the flow it would help.

Two are flat out, rest are balanced to maintain all radiators at roughly
the
same temperature drop.

If the others are closed almost down in an effort to get a reasonable
temperature drop across these two, it sould indicate inadequate
pipework for the size/distance of them.

I have been assuming the main reason for the closing down is most radiators
are fed from quite short runs from the pump/zone valves under the stairs
(shortest is 2m, longest about 5m, all in 15mm pipe) but these two
radiators are further away at the end of about 20m (10m each way) of 15mm
(plastic) pipe. For this reason they have their own pipe all the way back
to the zone valve.


You could look up the radiator manufacturer data for the radiators (or
ones close to them). There is not an enormous difference between
vendors for typical finned radiators. THe main effect is the number
of panels and which have fins. If you find something close in size,
you can scale it. This should give you a gross heat output assuming
the EN testing method. You then need to look at the derating table
for the mean water to air temperature correction factor. For 82
degree flow and 70 return, (MWTA about 55 degrees) the normal derating
is to multiply by 0.9. So if you determine by size that a radiator
has a nominal output of 1kW, its actual output under what should be
the design conditions for your system will be 900W. You can then
take that figure and plug it into the CDA method and just check that
the pipework to those two radiators is adequate for them. A rough
rule of thumb is that 15mm pipe should be good to carry 6kW over
distances of a few metres (but not 40 :-) ).

I think my worst case is the pair of radiators (about 3kW total) at around
20 m there and back of 15mm.


Beyond that, you could look through the design guide published by the
Copper Development Association and do the calculations for the pipe
runs.

http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf

If you plug in the numbers for the main pipe runs, that should give
some clue if there is something inadequate.

Thanks - will do. Sounds to be what I need.

It's slightly laborious but you don't have to be hugely accurate.

In effect, the system is adrift by a factor of 2:1, so it should be
possible to deduce what is going wrong. You can work back to
determine the pump requirement given the resistance and from that see
if it is within the range of the pump.


From a first pass I need a head of over 8m and the pump obviously isn't up
to that.

Can I put another pump in series on the return to the boiler to see if the
problem improves ? (i.e. do pump heads add ?)

Also I appear to be right on the velocity limit of the section of 22mm pipe
from the boiler. The article you quoted mentions long term erosion of the
pipe but does anything silly happen to the resistance effects of the pipe
for a quick test.

I'm thinking the proper solution is a separate pump at the boiler for
upstairs and downstairs systems with separate pipework as well,
unfortunately still with the 22mm length unless somebody knows where I can
get flexible 28mm pipe in 20 m lengths, but I'd like to get as much
understood with the current system before changing it.

Many thanks

Mike

"Mike" wrote in message
...
The recent very cold weather has thrown up a problem I hadn't noticed
until
now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more
than
enough to heat the house through about 20kW rated radiators.

Grant were one of the early entries into the Condensing oil boiler market
but are not one of the frequently encountered manufacturers up North at
least. Is your model a condenser or a non condenser?


And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about
65
degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a suspect
stat may be involved here, however your return water temperature appears to
show little variation between cut out and cut in on the boiler temperature.
This does suggest the rate of flow through the radiator system to be too
low.


Have tried the pump (Grundfos Alpha) in every position on it and all give
the same effect, though some vary the time taken that the boiler spends on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

I think you should get hold of a differential thermometer with sensetive
clip on probes or a non contact IR thermometer and check the differential
temperature across each radiator under steady-state conditions. If your
boiler is non-condensing the differential should be approximately
10/11degreesC.

If you study the FAQ on balancing a system it will help you to understand
the aims of balancing a system correctly and if your radiator load is as you
mention the performance should be closer to the expectations. Does your
assumed load include the hot water demand also or is that on top of your
figures?
You will find that the boiler will operate cyclically but with a higher flow
rate you may find the thermostat responds better because the water moves
more "actively" within the boiler, if not consider replacing the boiler
thermostat


Whereas in warmer weather I didn't really notice the radiators warming up
and cooling so much now it is obvious that they are continually heating up
and cooling down with the boiler.

This can be minimised by matching the boiler output to the load (trivial but
needs calibration and analysis equipment) but you will probably find that
balancing the system will give better comfort levels and once the house is
warmed up you will not be so conscious of variations

On Wed, 29 Dec 2004 21:54:11 -0000, "Mike" wrote:



I have been assuming the main reason for the closing down is most radiators
are fed from quite short runs from the pump/zone valves under the stairs
(shortest is 2m, longest about 5m, all in 15mm pipe) but these two
radiators are further away at the end of about 20m (10m each way) of 15mm
(plastic) pipe. For this reason they have their own pipe all the way back
to the zone valve.


OK. I think I'd contact the pipe manufacturer or see if it's on the
web site and see if you can get the equivalent figures to the CDA ones
for copper. I believe that plastic pipe has slightly narrower
internal bore and may also have different resistance behaviour. As
a first approximation, you could treat it as copper and plug the
numbers into the CDA formulae and see what you get.

It's good that they have their own home runs though.



You could look up the radiator manufacturer data for the radiators (or
ones close to them). There is not an enormous difference between
vendors for typical finned radiators. THe main effect is the number
of panels and which have fins. If you find something close in size,
you can scale it. This should give you a gross heat output assuming
the EN testing method. You then need to look at the derating table
for the mean water to air temperature correction factor. For 82
degree flow and 70 return, (MWTA about 55 degrees) the normal derating
is to multiply by 0.9. So if you determine by size that a radiator
has a nominal output of 1kW, its actual output under what should be
the design conditions for your system will be 900W. You can then
take that figure and plug it into the CDA method and just check that
the pipework to those two radiators is adequate for them. A rough
rule of thumb is that 15mm pipe should be good to carry 6kW over
distances of a few metres (but not 40 :-) ).

I think my worst case is the pair of radiators (about 3kW total) at around
20 m there and back of 15mm.

My gut feel is that that ought to be OK, but I'd run the numbers to
check.




Beyond that, you could look through the design guide published by the
Copper Development Association and do the calculations for the pipe
runs.

http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf

If you plug in the numbers for the main pipe runs, that should give
some clue if there is something inadequate.

Thanks - will do. Sounds to be what I need.

It's slightly laborious but you don't have to be hugely accurate.

In effect, the system is adrift by a factor of 2:1, so it should be
possible to deduce what is going wrong. You can work back to
determine the pump requirement given the resistance and from that see
if it is within the range of the pump.


From a first pass I need a head of over 8m and the pump obviously isn't up
to that.

Can I put another pump in series on the return to the boiler to see if the
problem improves ? (i.e. do pump heads add ?)

I don't believe they do, unfortunately. If you put in a more
powerful one then the first is going to end up making that worse I
think.



Also I appear to be right on the velocity limit of the section of 22mm pipe
from the boiler. The article you quoted mentions long term erosion of the
pipe but does anything silly happen to the resistance effects of the pipe
for a quick test.

I was afraid it might be. Unfortunately the plastic is a bit worse
than the copper as well. THe design point is to stay between 0.5 and
1.5m/sec, although sludging shouldn't be an issue if you are taking
care of the system with inhibitor. Beyond 1.5m/sec the noise level
increases but that may not be an issue if it's outside or under the
floor. However, the head required to increase the flow starts to
increase dramatically.





I'm thinking the proper solution is a separate pump at the boiler for
upstairs and downstairs systems with separate pipework as well,
unfortunately still with the 22mm length unless somebody knows where I can
get flexible 28mm pipe in 20 m lengths, but I'd like to get as much
understood with the current system before changing it.

It may be that the 28mm is adequate, especially if copper for this
amount of heat. Another option would be to run in two pairs of
22mm from the end of the 28mm and split those upstairs to downstairs.
it would be reasonably easy to calculate for that, but you could still
be towards the pump limit.

A second pump and pipe run would be the other option, and you could be
pretty confident of each working and adjustability for each as well.

I have never seen barrier pipe or even non-barrier in 28mm coils. You
could contact Hepworth or John Guest and see if they can do it to
order.





--

..andy

To email, substitute .nospam with .gl

"John" wrote in message
...

"Mike" wrote in message
...
The recent very cold weather has thrown up a problem I hadn't noticed
until now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more
than enough to heat the house through about 20kW rated radiators.

Grant were one of the early entries into the Condensing oil boiler market
but are not one of the frequently encountered manufacturers up North at
least. Is your model a condenser or a non condenser?

Non condensor


And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about
65 degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a suspect
stat may be involved here, however your return water temperature appears
to
show little variation between cut out and cut in on the boiler
temperature.
This does suggest the rate of flow through the radiator system to be too
low.

What should the stat limits be. The upper limit is programmable via a knob
on front of boiler but manual doesn't say if the lower limit is fixed or
moves with it.



Have tried the pump (Grundfos Alpha) in every position on it and all
give
the same effect, though some vary the time taken that the boiler spends
on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

I think you should get hold of a differential thermometer with sensetive
clip on probes or a non contact IR thermometer and check the differential
temperature across each radiator under steady-state conditions. If your
boiler is non-condensing the differential should be approximately
10/11degreesC.

Am using a Maplin non contact IR. As the system has three CH zones I think
in better weather it got the system up to temp and then everything was ok.
But now under heavy load it can't get there.


If you study the FAQ on balancing a system it will help you to understand
the aims of balancing a system correctly and if your radiator load is as
you
mention the performance should be closer to the expectations.

That was what I used. Most helpful. I thought I had got the system to
around 80 deg in, 65 out for most radiators but as it turns out this was
only when the room thermostats were being overridden one by one.


Does your assumed load include the hot water demand also or is that on top
of your
figures?

There is provision for a hot water feed but it is currently not activated as
I am going to be using a small hydroelectric generator to drive the
immersion heater so hopefully the boiler won't be called upon for this.

Thanks

Mike

"Andy Hall" wrote in message
...
I have never seen barrier pipe or even non-barrier in 28mm coils. You
could contact Hepworth or John Guest and see if they can do it to
order.

Tried a while back with no joy. Speedfit rep couldn't understand why not
since they do the 32mm MDPE (?) in large coils of course.

"Andy Hall" wrote in message
...
On Wed, 29 Dec 2004 20:16:35 -0000, "Mike" wrote:

The recent very cold weather has thrown up a problem I hadn't noticed
until
now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more
than
enough to heat the house through about 20kW rated radiators.

And indeed it did when the weather wasn't so cold outside. But now it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is about
65
degC plus or minus a degree or two.

Have tried the pump (Grundfos Alpha) in every position on it and all give
the same effect, though some vary the time taken that the boiler spends
on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

Whereas in warmer weather I didn't really notice the radiators warming up
and cooling so much now it is obvious that they are continually heating
up
and cooling down with the boiler.


Arrangement is


|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |


|--------------------------------------------------------|----------|---|-
-
-|

Only unusual thing is the length of pipe between the boiler and pump -
about
40 metres due to position of boiler in an outbuilding. Obviously it's
40m
back as well.
But temperature drop across this very well lagged pipe appears to be a
degree at most.

My guess is the pump doesn't circulate enough water and was thinking of
putting another pump in the return :

40m
|------------------------ pump----4 zone valves to HW and 3 CH zones
Boiler
| | | |
|------------------------
ump ------------------------|----------|---|---|
40m

Should this help ?

Any alternative suggestions or routes to investigate gratefully received.

Many thanks

Mike


Basically the flow rate is too low, as is the return temperature. You
have about 25 degrees temperature drop on a design that should be
about 12 degrees.

I turned off the upstairs system and with the Alpha near max on the variable
pot settings, the return temperature went up to 76 deg. So it would appear
the pipe cannot source upstairs and downstairs so I'll need another parallel
pump and set of pipes from the boiler to upstairs.

However, even with the return temp correct, the thermostat still has a huge
hysteresis. It turns off at about 90 deg C but doesn't restart until the
output temperature drops to about 75 degC. At this point the input
temperature is still the same, i.e. a degree higher going into the boiler
than coming out, presumably due to the large thermal mass of the water in
the system.

Grant are "on holiday" until the New Year. Any idea what hysteresis an oil
boiler control thermostat should have ?

Thanks

Mike

"Mike" wrote in message
...

"John" wrote in message
...

"Mike" wrote in message
...
The recent very cold weather has thrown up a problem I hadn't noticed
until now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be more
than enough to heat the house through about 20kW rated radiators.

Grant were one of the early entries into the Condensing oil boiler market
but are not one of the frequently encountered manufacturers up North at
least. Is your model a condenser or a non condenser?

Non condensor


And indeed it did when the weather wasn't so cold outside. But now
it's
colder it can't keep up. Have traced the problem to the boiler output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is
about
65 degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a
suspect
stat may be involved here, however your return water temperature appears
to
show little variation between cut out and cut in on the boiler
temperature.
This does suggest the rate of flow through the radiator system to be too
low.

What should the stat limits be. The upper limit is programmable via a
knob
on front of boiler but manual doesn't say if the lower limit is fixed or
moves with it.


You will need to ask Grant for this info but some boiler stats have a small
differential adjustment screw concealed about the body somewhere. I'd try to
be certain that the flow rates through the boiler are adequate before
upsetting the factory adjustment of this though



Have tried the pump (Grundfos Alpha) in every position on it and all
give
the same effect, though some vary the time taken that the boiler spends
on
or off. But typically it is 2-3 mins on, 3-4 mins off. Obviously if I
could get it to be on a bit longer and off less the house would be warm
again.

I think you should get hold of a differential thermometer with sensetive
clip on probes or a non contact IR thermometer and check the differential
temperature across each radiator under steady-state conditions. If your
boiler is non-condensing the differential should be approximately
10/11degreesC.

Am using a Maplin non contact IR. As the system has three CH zones I
think
in better weather it got the system up to temp and then everything was ok.
But now under heavy load it can't get there.


If you study the FAQ on balancing a system it will help you to understand
the aims of balancing a system correctly and if your radiator load is as
you
mention the performance should be closer to the expectations.

That was what I used. Most helpful. I thought I had got the system to
around 80 deg in, 65 out for most radiators but as it turns out this was
only when the room thermostats were being overridden one by one.

I'd try turning all your stats full up so that all rads are operating
together before balancing the system and then go for a lower differential
across them say about 10/11 degrees C. As zones close down on the stats the
pump head will increase marginally (circulators are centrifugal) subject to
the response of the Alpha. Increased head will give a slightly faster flow
which in turn will reduce the differential tamp across the rads but not by
much. The reduced Dt will give a higher mean rad temp which will be to your
advantage



Does your assumed load include the hot water demand also or is that on
top
of your
figures?

There is provision for a hot water feed but it is currently not activated
as
I am going to be using a small hydroelectric generator to drive the
immersion heater so hopefully the boiler won't be called upon for this.

Sounds good - do you live near a fast flowing stream? I have a hankering to
move somewhere hilly with a rushing torrent when I retire and do something
similar. If the water is pure I'll install a sandfilter and UV unit to
become more or less self sufficient energy and water wise at least



Thanks

Mike

"John" wrote in message
...
The recent very cold weather has thrown up a problem I hadn't noticed
until now.

Boiler is a Grant 70/90 Euroflame and it's 25 kW output should be
more
than enough to heat the house through about 20kW rated radiators.
And indeed it did when the weather wasn't so cold outside. But now
it's colder it can't keep up. Have traced the problem to the boiler
output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is
about 65 degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a
suspect
stat may be involved here, however your return water temperature
appears
to
show little variation between cut out and cut in on the boiler
temperature.
This does suggest the rate of flow through the radiator system to be
too
low.

What should the stat limits be. The upper limit is programmable via a
knob
on front of boiler but manual doesn't say if the lower limit is fixed or
moves with it.


You will need to ask Grant for this info but some boiler stats have a
small
differential adjustment screw concealed about the body somewhere. I'd try
to
be certain that the flow rates through the boiler are adequate before
upsetting the factory adjustment of this though

They're "on holiday" until Jan 4th :-(


There is provision for a hot water feed but it is currently not
activated
as
I am going to be using a small hydroelectric generator to drive the
immersion heater so hopefully the boiler won't be called upon for this.

Sounds good - do you live near a fast flowing stream? I have a hankering
to
move somewhere hilly with a rushing torrent when I retire and do something
similar. If the water is pure I'll install a sandfilter and UV unit to
become more or less self sufficient energy and water wise at least

Yeah - we have a farm in the Peak District. There is a spring at the top of
the hill which needs a 10micron, 0.5 micron, then UV filter to make it
anything like safe to drink. But we could probably put it in a bottle as is
and sell it as mineral water :-)

As for stream, we have a good flowing stream running along the side of us.
Total drop on our land is 10m but that would rather a major dam so will try
to achieve about 5 feet which will yield around 2 to 3kW for the hot water
and charging batteries when the mains goes (every few weeks).

Hope you find something similar.

"Mike" wrote in message
...


SNIP
.. Have traced the problem to the boiler
output
temperature rising up to the cut-off limit (just under 90 degC) then
turning
off until the pump circulates the water enough for it to drop to the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is
about 65 degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a
suspect
stat may be involved here, however your return water temperature
appears
to
show little variation between cut out and cut in on the boiler
temperature.
This does suggest the rate of flow through the radiator system to be
too
low.

What should the stat limits be. The upper limit is programmable via a
knob
on front of boiler but manual doesn't say if the lower limit is fixed
or
moves with it.


You will need to ask Grant for this info but some boiler stats have a
small
differential adjustment screw concealed about the body somewhere. I'd try
to
be certain that the flow rates through the boiler are adequate before
upsetting the factory adjustment of this though

They're "on holiday" until Jan 4th :-(


A thought occurs to me regarding temperature gradients through the boiler
shell. Most boilers have tappings for flow and return at either side of the
boiler. Some boilers are not happy if flow and return are connected to the
same side of the boiler as it "can" lead to still water (or at least slow to
move around) conditions surrounding the thermostat phial. What piping
arrangement do you have and does it agree with reccomendations in the
Installation and /service booklet for your boiler?
I would expect a replacement thermostat to be in the region of £20.00 or so
unless its a special. Most boilers seem to use a Ranco model stat

"John" wrote in message
...


SNIP
. Have traced the problem to the boiler
output
temperature rising up to the cut-off limit (just under 90 degC)
then
turning
off until the pump circulates the water enough for it to drop to
the
turn-on
value (appears to be around 75 degC).

With the boiler in it's on or off state, the return temperature is
about 65 degC plus or minus a degree or two.


The hysteresis your stat exhibits is perhaps a bit excessive and a
suspect
stat may be involved here, however your return water temperature
appears
to
show little variation between cut out and cut in on the boiler
temperature.
This does suggest the rate of flow through the radiator system to be
too
low.

What should the stat limits be. The upper limit is programmable via
a
knob
on front of boiler but manual doesn't say if the lower limit is fixed
or
moves with it.


You will need to ask Grant for this info but some boiler stats have a
small
differential adjustment screw concealed about the body somewhere. I'd
try
to
be certain that the flow rates through the boiler are adequate before
upsetting the factory adjustment of this though

They're "on holiday" until Jan 4th :-(


A thought occurs to me regarding temperature gradients through the boiler
shell. Most boilers have tappings for flow and return at either side of
the
boiler. Some boilers are not happy if flow and return are connected to the
same side of the boiler as it "can" lead to still water (or at least slow
to
move around) conditions surrounding the thermostat phial. What piping
arrangement do you have and does it agree with reccomendations in the
Installation and /service booklet for your boiler?

I did wonder this. There are tappings each side but it does specifically
mention it is OK to use just one side if you are in a corner. But the
thermostat pocket is in the top corner away from the tappings being used.


I would expect a replacement thermostat to be in the region of £20.00 or
so
unless its a special. Most boilers seem to use a Ranco model stat

Only had it a few months so if it's dead I want a new one from them :-)

Many thanks

"John" wrote in message
...
SNIP

boiler. Some boilers are not happy if flow and return are connected to
the
same side of the boiler as it "can" lead to still water (or at least
slow
to
move around) conditions surrounding the thermostat phial. What piping
arrangement do you have and does it agree with reccomendations in the
Installation and /service booklet for your boiler?

I did wonder this. There are tappings each side but it does
specifically
mention it is OK to use just one side if you are in a corner. But the
thermostat pocket is in the top corner away from the tappings being
used.


I would not be surprised if the temperature swings are related to just
this
point. Is it going to be difficult to route the flow pipe over the top of
the boiler into the opposite corner so as to create some water movement
around the phial?
Have you tried taking temperature readings of the boiler around the
thermostat phial to see if there is a "dead spot" giving rise to this
lagging response
Also, it may be possible if your boiler has two pockets or phials to
relocate the sensor to the other pocket. Some boilers have two seperate
capillaries (control and overheat) with pockets at opposite sides of the
water jacket.


However you could also withdraw the unit from the phial and with
pan of water, hob, thermometer and a multimeter check the actual response
of
the stat out of the boiler.
Having more info available will speed any reponse you do get from Grant

Thanks for this suggestion which I've just done. Unit switches off at
80degC and back on at around 65 deg. I assume therefore there is a 10 deg
drop in the pocket but there still appears to be a huge hysteresis outside
of the boiler.

The boiler itself appears well insulated but I couldn't find more than a
degree or two difference side to side.

Roll on Grant coming back on Jan 4th.