I recently moved into a house and I've successfully upgraded the CH/HW
controls to an 'S-Plan' type system (see previous posts). My
modifications only required me to replace a mechanical timeswitch with
a programmer, thermostats and 2-port zone valves. In other words, I
pretty much ignored what was in the external boiler housing and
replaced the single mech timer with some more elaborate switching
gubbins.

Over the weekend, I noticed something that I think is a bit odd. The
external boiler housing contains the oil-fired boiler (warmflow, no
pump overrun required) and a circulating pump on the feed. However, the
pump seems to be wired _after_ the boiler thermostat (a small gray box
with a knob from 1..5 that supplies mains power to the burnber unit).
It strikes me that this is odd and potentially damaging. Surely the
circulating pump should be circulating water when either the CH or HW
zones require heat, not just when the boiler is in the part of its
cycle that fires the burner.

Does what I've described sound normal? Or should I rewire the
circulating pump?

Cheers,
Jonathan

In an earlier contribution to this discussion,
Jonathan wrote:

I recently moved into a house and I've successfully upgraded the CH/HW
controls to an 'S-Plan' type system (see previous posts). My
modifications only required me to replace a mechanical timeswitch with
a programmer, thermostats and 2-port zone valves. In other words, I
pretty much ignored what was in the external boiler housing and
replaced the single mech timer with some more elaborate switching
gubbins.

Over the weekend, I noticed something that I think is a bit odd. The
external boiler housing contains the oil-fired boiler (warmflow, no
pump overrun required) and a circulating pump on the feed. However,
the pump seems to be wired _after_ the boiler thermostat (a small
gray box with a knob from 1..5 that supplies mains power to the
burnber unit). It strikes me that this is odd and potentially
damaging. Surely the circulating pump should be circulating water
when either the CH or HW zones require heat, not just when the boiler
is in the part of its cycle that fires the burner.

Does what I've described sound normal? Or should I rewire the
circulating pump?

Cheers,
Jonathan

The pump should be running whenever the *external* controls are telling the
boiler to fire - even when it's own internal thermostat is telling it not
to.

It you wire it up according to the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm it will be fine!

In brief, the timer and room stat control the CH zone valve. The timer and
cylinder stat control the HW zone valve. Whenever either or both zone valves
are open, power is supplied to the boiler and pump, in *parallel*.
--
Cheers,
Set Square
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Set Square wrote:
The pump should be running whenever the *external* controls are telling the
boiler to fire - even when it's own internal thermostat is telling it not
to.

It you wire it up according to the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm it will be fine!

Thanks. That confirms what I thought. I'll re-wire it the way it should
be.

Jonathan

In article ,
Set Square wrote:
The pump should be running whenever the *external* controls are telling
the boiler to fire - even when it's own internal thermostat is telling
it not to.

It you wire it up according to the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm it will be fine!

In brief, the timer and room stat control the CH zone valve. The timer
and cylinder stat control the HW zone valve. Whenever either or both
zone valves are open, power is supplied to the boiler and pump, in
*parallel*.

The slight problem with this design is that if the boiler is firing when
the room or cylinder stat are both satisfied, when shut down it may kettle.
IN which case a simple pump over-run circuit is needed.

--
*You sound reasonable......time to up my medication

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Set Square wrote:
The pump should be running whenever the *external* controls are telling
the boiler to fire - even when it's own internal thermostat is telling
it not to.

It you wire it up according to the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm it will be fine!

In brief, the timer and room stat control the CH zone valve. The timer
and cylinder stat control the HW zone valve. Whenever either or both
zone valves are open, power is supplied to the boiler and pump, in
*parallel*.

The slight problem with this design is that if the boiler is firing when
the room or cylinder stat are both satisfied, when shut down it may kettle.
IN which case a simple pump over-run circuit is needed.

--
*You sound reasonable......time to up my medication

Dave Plowman London SW
To e-mail, change noise into sound.

I don't believe kettling is a problem in this case, and my fix should
only cause the pump to ru nmore than it does now (specifically, when
the zone valves tell the boiler to fire but the boiler's thermostat is
telling it not to). But I'll bear in mind what you've said .....

"Dave Plowman (News)" wrote in message
...
In article ,
Set Square wrote:
The pump should be running whenever the *external* controls are telling
the boiler to fire - even when it's own internal thermostat is telling
it not to.

It you wire it up according to the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm it will be fine!

In brief, the timer and room stat control the CH zone valve. The timer
and cylinder stat control the HW zone valve. Whenever either or both
zone valves are open, power is supplied to the boiler and pump, in
*parallel*.

The slight problem with this design is that if the boiler is firing when
the room or cylinder stat are both satisfied, when shut down it may
kettle.
IN which case a simple pump over-run circuit is needed.

The senility has set in. He said the makers say it doesn't need a pump
over-run.

In article ,
Doctor Evil wrote:
The slight problem with this design is that if the boiler is firing
when the room or cylinder stat are both satisfied, when shut down it
may
kettle.
IN which case a simple pump over-run circuit is needed.

The senility has set in. He said the makers say it doesn't need a pump
over-run.

Good grief - you've actually fully read a post and understood it.

Google readers, this is a first.

But why aren't you recommending it's all replaced with some Japanese gismo?

--
*It sounds like English, but I can't understand a word you're saying.

Dave Plowman London SW
To e-mail, change noise into sound.

In article .com,
Jonathan wrote:
The slight problem with this design is that if the boiler is firing
when the room or cylinder stat are both satisfied, when shut down it
may kettle. IN which case a simple pump over-run circuit is needed.


I don't believe kettling is a problem in this case, and my fix should
only cause the pump to ru nmore than it does now (specifically, when
the zone valves tell the boiler to fire but the boiler's thermostat is
telling it not to). But I'll bear in mind what you've said .....

Apologies. Your boiler already must have some provision for this, if it
says no over-run needed.

--
*Why are they called apartments, when they're all stuck together? *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Evil wrote:
The slight problem with this design is that if the boiler is firing
when the room or cylinder stat are both satisfied, when shut down it
may
kettle.
IN which case a simple pump over-run circuit is needed.

The senility has set in. He said the makers say it doesn't need a pump
over-run.

Good grief - you've actually fully read a post and understood it.

You obviously can't do that.

Dave Plowman (News) wrote:
In article .com,
Jonathan wrote:
The slight problem with this design is that if the boiler is firing
when the room or cylinder stat are both satisfied, when shut down it
may kettle. IN which case a simple pump over-run circuit is needed.


I don't believe kettling is a problem in this case, and my fix should
only cause the pump to ru nmore than it does now (specifically, when
the zone valves tell the boiler to fire but the boiler's thermostat is
telling it not to). But I'll bear in mind what you've said .....

Apologies. Your boiler already must have some provision for this, if it
says no over-run needed.

Your point is still relevant though for another reason. As an external
boiler, there should really be a frost thermostat, which there doesn't
seem to be (based on the wiring installed by the builders), but that's
a whole other story!

Incidentally, the symptoms that led me to check the pump wiring were
(i) what I felt were unusually long times between boiler fire cycles
(due to hot water not being cleared from the boiler) and (ii) a need to
have the boiler thermostst near its maximum setting (although this
probably isn't the right time to test this in Ireland, given the recent
weather!). Do these symptoms make sense, given the problem I described
with the pump wiring?

In article .com,
Jonathan wrote:
Incidentally, the symptoms that led me to check the pump wiring were
(i) what I felt were unusually long times between boiler fire cycles
(due to hot water not being cleared from the boiler) and (ii) a need to
have the boiler thermostst near its maximum setting (although this
probably isn't the right time to test this in Ireland, given the recent
weather!). Do these symptoms make sense, given the problem I described
with the pump wiring?

Well, neither the C or S plan allow any feedback from the boiler or
provide any over-run, unless I'm missing something.

So there's no way the boiler can know in advance when its services are no
longer required. So I presume it has a fast acting shut off to prevent
kettling and a heat exchanger made out of a low thermal capacity material,
-ie not cast iron.

But I'm only surmising as I don't know anything about oil boilers.

It's simple enough to bring the temperature of the water stored in the
boiler down - simply clamp a cylinder stat with changeover contacts wired
to break at low rather than high - most do - to the output pipe so that it
keeps the pump running until the desired lower temp in the boiler is
reached. Although I simply built a timer which runs the pump for a couple
of minutes after everything is shut down as it made for easier wiring in
my case.

--
*Am I ambivalent? Well, yes and no.

Dave Plowman London SW
To e-mail, change noise into sound.

In an earlier contribution to this discussion,
Jonathan wrote:


Incidentally, the symptoms that led me to check the pump wiring were
(i) what I felt were unusually long times between boiler fire cycles
(due to hot water not being cleared from the boiler) and (ii) a need
to have the boiler thermostst near its maximum setting (although this
probably isn't the right time to test this in Ireland, given the
recent weather!). Do these symptoms make sense, given the problem I
described with the pump wiring?

If by (ii) you mean that your DHW didn't get hot unless you turned the
boiler stat UP, I would agree. When heating the water, your hot cylinder
probably can't absorb heat as fast as the boiler can produce it - with the
result that the boiler needs to cycle on and off. BUT the pump must run
until the cylinder stat is satisfied - even when the flame isn't on -
otherwise the water won't continue to heat once the boiler stat has opened.

(i) sounds reasonable too - because with no pump the hot water *inside* the
boiler won't get taken away - and will stay hot for a long time, causing the
boiler stat to stay open.
--
Cheers,
Set Square
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