A question from a novice...

My central heating system stopped supplyiing hot water this week. I
find that I can only get the boiler and pump to start if I also have
the heating on (which I don't really want at the moment). If I turn
only the hot water on, the boiler and pump don't start up. To make
matters worse, my immersion heater seems to be broken too.

The system is very old (probably about as old as the house - about 30
years). The boiler is a Concord WRS.

The electrics seem to be controlled by an unusual 10" square unit on
the wall next to the boiler. This is a "Fuel Guardian" (by Fuel
Economy Systems South Ltd). This unit has auto/off/override buttons
for both hot water and heating, and LED's for "Boiler On" and "Pump
On". Both buttons are set to "auto".

I can't locate a motorised valve anywhere. The h/w cylinder is on the
top floor of the house - directly above the boiler, which is on the
floor below. There's no valve in or around the cylinder, nor in the
space above the boiler.

Does anyone have any idea why I can only get hot water when the
heating is on? This was not the case until a few days ago.

Also, does anyone know anything about the "Fuel Guardian" unit - i.e.
what does it do, and how likely is it that it can be repaired if
faulty?

In an earlier contribution to this discussion,
ITM wrote:

A question from a novice...

My central heating system stopped supplyiing hot water this week. I
find that I can only get the boiler and pump to start if I also have
the heating on (which I don't really want at the moment). If I turn
only the hot water on, the boiler and pump don't start up. To make
matters worse, my immersion heater seems to be broken too.

The system is very old (probably about as old as the house - about 30
years). The boiler is a Concord WRS.

The electrics seem to be controlled by an unusual 10" square unit on
the wall next to the boiler. This is a "Fuel Guardian" (by Fuel
Economy Systems South Ltd). This unit has auto/off/override buttons
for both hot water and heating, and LED's for "Boiler On" and "Pump
On". Both buttons are set to "auto".

I can't locate a motorised valve anywhere. The h/w cylinder is on the
top floor of the house - directly above the boiler, which is on the
floor below. There's no valve in or around the cylinder, nor in the
space above the boiler.

Does anyone have any idea why I can only get hot water when the
heating is on? This was not the case until a few days ago.

Also, does anyone know anything about the "Fuel Guardian" unit - i.e.
what does it do, and how likely is it that it can be repaired if
faulty?

I don't know this specific system but - from your description - I would
hazard a guess that you have a gravity HW and pumped CH system.

In HW mode, the boiler is supposed to fire but the pump doesn't run. The hot
water gets hot by gravity (convection) circulation, but the radiators remain
cold. There is almost certainly *not* a thermostat on the HW cylinder (other
than one which is part of the immersion heater).

In CH mode, the boiler is supposed to fire *and* the pump is supposed to
run - circulating hot water round the radiators. There may be a room
thermostat which turns the pump off when the house gets warm. It is unlikely
that this also turns the boiler off - so that the boiler will simply cycle
(rather inefficiently!) on its own thermostat when no heating is required.

If the boiler *doesn't* come on in HW mode but *does* in CH mode, there is
something wrong with the programmer and/or wiring.

*Is* there a room stat?
If so, when you turn it down, does the pump stop? Does the boiler also stop?

Assuming that the pump does stop but the boiler doesn't, a short term
solution might be to run in CH mode with the room stat turned right down.
You should then get some hot water. You'll still need to find the *real*
problem - but not quite so urgently.

If there *isn't* a room stat, you could achieve the same thing by
temporarily disconnecting (and making safe!) the wiring to the pump.

--
Cheers,
Set Square
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On Sun, 25 Jul 2004 18:44:54 +0100, "Set Square"
wrote:

I don't know this specific system but - from your description - I would
hazard a guess that you have a gravity HW and pumped CH system.

In HW mode, the boiler is supposed to fire but the pump doesn't run. The hot
water gets hot by gravity (convection) circulation, but the radiators remain
cold. There is almost certainly *not* a thermostat on the HW cylinder (other
than one which is part of the immersion heater).

There is actually a thermostat on the HW cylinder, and it's connected
to the "Fuel Guardian" box

In CH mode, the boiler is supposed to fire *and* the pump is supposed to
run - circulating hot water round the radiators. There may be a room
thermostat which turns the pump off when the house gets warm. It is unlikely
that this also turns the boiler off - so that the boiler will simply cycle
(rather inefficiently!) on its own thermostat when no heating is required.

If the boiler *doesn't* come on in HW mode but *does* in CH mode, there is
something wrong with the programmer and/or wiring.

That's exactly what's happening, but it's started happening overnight,
so something somewhere has broken (it's been fine for years before)

*Is* there a room stat?
If so, when you turn it down, does the pump stop? Does the boiler also stop?


Yes, there's a room stat. If I turn it down the pump stops, but the
boiler doesn't.

Assuming that the pump does stop but the boiler doesn't, a short term
solution might be to run in CH mode with the room stat turned right down.
You should then get some hot water. You'll still need to find the *real*
problem - but not quite so urgently.

I've tried that, but if the room stat is turned right down, and I
switch on both C/H and Hot Water, neither the boiler nor the pump
starts up. The "Boiler" light on the Fuel Guardian does switch on,
though. In any case, I get no hot water.

If there *isn't* a room stat, you could achieve the same thing by
temporarily disconnecting (and making safe!) the wiring to the pump.

In an earlier contribution to this discussion,
ITM wrote:

On Sun, 25 Jul 2004 18:44:54 +0100, "Set Square"
wrote:


There is actually a thermostat on the HW cylinder, and it's connected
to the "Fuel Guardian" box

What is this stat set to? Has it accidentally been turned down or off?


*Is* there a room stat?
If so, when you turn it down, does the pump stop? Does the boiler
also stop?


Yes, there's a room stat. If I turn it down the pump stops, but the
boiler doesn't.

If the room stat is turned right down, and I
switch on both C/H and Hot Water, neither the boiler nor the pump
starts up. The "Boiler" light on the Fuel Guardian does switch on,
though. In any case, I get no hot water.

But what happens if you just switch on CH and *not* HW, with the room stat
turned down? If you can make the boiler fire, you should get gravity hot
water - even if the official HW switch is off!

--
Cheers,
Set Square
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On Sun, 25 Jul 2004 20:52:41 +0100, "Set Square"
wrote:

There is actually a thermostat on the HW cylinder, and it's connected
to the "Fuel Guardian" box

What is this stat set to? Has it accidentally been turned down or off?

This is set to 60 degrees (was higher)


If the room stat is turned right down, and I
switch on both C/H and Hot Water, neither the boiler nor the pump
starts up. The "Boiler" light on the Fuel Guardian does switch on,
though. In any case, I get no hot water.

But what happens if you just switch on CH and *not* HW, with the room stat
turned down? If you can make the boiler fire, you should get gravity hot
water - even if the official HW switch is off!

With the room stat turned down I can't get the boiler to fire up at
all.

What I don't understand is how I can get gravity hot water if the
cylinder is above the boiler and there's no pump working?

In an earlier contribution to this discussion,
ITM wrote:

On Sun, 25 Jul 2004 20:52:41 +0100, "Set Square"
wrote:

There is actually a thermostat on the HW cylinder, and it's
connected to the "Fuel Guardian" box

What is this stat set to? Has it accidentally been turned down or
off?

This is set to 60 degrees (was higher)


If the room stat is turned right down, and I
switch on both C/H and Hot Water, neither the boiler nor the pump
starts up. The "Boiler" light on the Fuel Guardian does switch on,
though. In any case, I get no hot water.

But what happens if you just switch on CH and *not* HW, with the
room stat turned down? If you can make the boiler fire, you should
get gravity hot water - even if the official HW switch is off!

With the room stat turned down I can't get the boiler to fire up at
all.

In your previous reply, you appeared to be saying that - with CH running -
if you turned down the room stat, the pump stopped but the boiler didn't.
Can you still do this - because all you need is the boiler to run.


What I don't understand is how I can get gravity hot water if the
cylinder is above the boiler and there's no pump working?

That's how gravity (sometimes called "thermo-syphon") circulation works. The
water at the top of the boiler is a bit hotter than the water lower down,
and thus less dense. This "floats" up the flow pipe to the indirect coil
inside the hot water cylinder - where it transfers heat to the hot water in
the tank, cools down, and flows back down the return pipe to the bottom of
the boiler.

If your system is designed for gravity hot water circulation (and I'm still
not *totally* sure whether it is!) and has suitable pipe sizing (usually
28mm or imperial sized 1" pipe) you don't a pump in HW-only mode - with the
pump only being used for CH.

--
Cheers,
Set Square
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On Sun, 25 Jul 2004 21:50:23 +0100, "Set Square"
wrote:

In your previous reply, you appeared to be saying that - with CH running -
if you turned down the room stat, the pump stopped but the boiler didn't.
Can you still do this - because all you need is the boiler to run.

Yes I can still do this, but the stat needs to be turned up in the
first place to get the boiler started. That's my immediate problem -
in order to get the hot water coming on automatically in the morning
I've set the heating to come on with it. The problem is that the
heating won't fire up the boiler unless the thermostat is turned up -
not great in the middle of summer, as I have a couple of bathroom
radiators which I can't turn off!

That's how gravity (sometimes called "thermo-syphon") circulation works. The
water at the top of the boiler is a bit hotter than the water lower down,
and thus less dense. This "floats" up the flow pipe to the indirect coil
inside the hot water cylinder - where it transfers heat to the hot water in
the tank, cools down, and flows back down the return pipe to the bottom of
the boiler.

If your system is designed for gravity hot water circulation (and I'm still
not *totally* sure whether it is!) and has suitable pipe sizing (usually
28mm or imperial sized 1" pipe) you don't a pump in HW-only mode - with the
pump only being used for CH.

Thanks for the explanation - makes perfect sense. Would the lack of a
motorised valve suggest that I have a gravity HW system?

The big question is: why can't I get the boiler started by switching
on just the hot water any more. My guess is that the electrics in the
"Fuel Guardian" box may have developed a fault, but I really wouldn't
know how to start investigating.

In an earlier contribution to this discussion,
ITM wrote:

The problem is that the
heating won't fire up the boiler unless the thermostat is turned up -
not great in the middle of summer, as I have a couple of bathroom
radiators which I can't turn off!

It gets mysteriouser!


Thanks for the explanation - makes perfect sense. Would the lack of a
motorised valve suggest that I have a gravity HW system?

Yes it would - but I'm puzzled as to what the cylinder stat does - 'cos you
don't usually have one unless there is a motorised valve. Also the fact that
the boiler keeps going when the pump stops suggests that it *isn't * fully
pumped - which again suggests gravity hot water.

The big question is: why can't I get the boiler started by switching
on just the hot water any more. My guess is that the electrics in the
"Fuel Guardian" box may have developed a fault, but I really wouldn't
know how to start investigating.

I've done a Google search on "Fuel Guardian" and "Fuel Economy Systems
South" to no avail! Have you looked inside the control box? My guess is that
there are some relays inside, and that it attempts to provide a poor man's
boiler interlock - to turn the boiler off when the demands are satisfied
(although it can't totally achieve that without valves). If a relay had
failed it would probably prevent the heating from working. Worth
investigating, anyway!

If all else fails, you could throw away this box and install a conventional
programmer - but this won't use the cylinder stat unless you also install a
motorised valve. If you *do* include a valve, you can have a C-Plan system
with full boiler interlock. [See
http://content.honeywell.com/uk/homes/systems.htm ]

--
Cheers,
Set Square
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On Sun, 25 Jul 2004 22:52:38 +0100, "Set Square"
wrote:

I've done a Google search on "Fuel Guardian" and "Fuel Economy Systems
South" to no avail! Have you looked inside the control box? My guess is that
there are some relays inside, and that it attempts to provide a poor man's
boiler interlock - to turn the boiler off when the demands are satisfied
(although it can't totally achieve that without valves). If a relay had
failed it would probably prevent the heating from working. Worth
investigating, anyway!

I've looked inside, and there are a couple of relays in there. The
trouble is that I can't find a supplier for this unit (I also tried
Google to no avail!)

If all else fails, you could throw away this box and install a conventional
programmer - but this won't use the cylinder stat unless you also install a
motorised valve. If you *do* include a valve, you can have a C-Plan system
with full boiler interlock. [See
http://content.honeywell.com/uk/homes/systems.htm ]

I do have a conventional programmer - it's connected to the Fuel
Guardian box. That's why I can't work out the purpose of this
mysterious box!

"ITM" wrote in message
...
On Sun, 25 Jul 2004 22:52:38 +0100, "Set Square"
wrote:

I've done a Google search on "Fuel Guardian" and "Fuel Economy Systems
South" to no avail! Have you looked inside the control box? My guess is
that
there are some relays inside, and that it attempts to provide a poor
man's
boiler interlock - to turn the boiler off when the demands are satisfied
(although it can't totally achieve that without valves). If a relay had
failed it would probably prevent the heating from working. Worth
investigating, anyway!

I've looked inside, and there are a couple of relays in there. The
trouble is that I can't find a supplier for this unit (I also tried
Google to no avail!)

If all else fails, you could throw away this box and install a
conventional
programmer - but this won't use the cylinder stat unless you also install
a
motorised valve. If you *do* include a valve, you can have a C-Plan
system
with full boiler interlock. [See
http://content.honeywell.com/uk/homes/systems.htm ]

I do have a conventional programmer - it's connected to the Fuel
Guardian box. That's why I can't work out the purpose of this
mysterious box!

Just a guess - but a major issue with a gravity system is that the hot water
heats to the temperature set on the boiler thermostat. It could be that (on
gravity HW only) your cylinder thermostat and the 'fuel guardian' system
will stop the boiler firing once the cylinder thermostat hits the correct
hot water temperature (although that still won't work if the CH is running).
At least it would stop the boiler cycling on and off repeatedly once the HW
was up to temperature (which wastes fuel).

If this is the case then a faulty cylinder thermostat could possibly cause
the symptoms you are experiencing.

You could try turning the thermostat up and/or moving it away from the side
of the cylinder - just in case it is partially working but shutting off at
too low a temperature.

HTH
Dave R

In an earlier contribution to this discussion,
ITM wrote:


I've looked inside, and there are a couple of relays in there. The
trouble is that I can't find a supplier for this unit (I also tried
Google to no avail!)

Are the relays removeable - i.e. plugged into sockets? If so, take then out
and in a few times to make sure they are contacting properly. If that
doesn't fix it, swap them round - assuming they are the same as each other -
and see whether the symptoms change.

In my view, these are now your prime suspects. You can probably get
replacements if they are broken - I expect they are generic, and not
specific to the firm which made the control box. Are you able to test them -
or do you know a man who can?

If all else fails, replace this black box with a conventional CH junction
box in order to connect the programmer, boiler, pump and room stat in the
normal way. As I said before, you won't then be able to use the cyl stat -
unless you add a zone valve and convert it to a C-Plan system.
--
Cheers,
Set Square
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In an earlier contribution to this discussion,
David W.E. Roberts wrote:


Just a guess - but a major issue with a gravity system is that the
hot water heats to the temperature set on the boiler thermostat. It
could be that (on gravity HW only) your cylinder thermostat and the
'fuel guardian' system will stop the boiler firing once the cylinder
thermostat hits the correct hot water temperature (although that
still won't work if the CH is running). At least it would stop the
boiler cycling on and off repeatedly once the HW was up to
temperature (which wastes fuel).

If this is the case then a faulty cylinder thermostat could possibly
cause the symptoms you are experiencing.

You could try turning the thermostat up and/or moving it away from
the side of the cylinder - just in case it is partially working but
shutting off at too low a temperature.


Yes, this is my guess too - that it's a partial boiler interlock, to stop
the boiler needlessly cycling in HW mode. As you say, it won't stop the HW
getting too hot when the CH is on!

It *could* be the cylinder stat in which case shorting the wires (assuming
it's a normally closed switch which opens when the set temperature is
reached) may achieve a short-term work-around.

My feeling though is that it's a duff relay in the control box. One of the
odd things is that, to get the boiler running, the room stat has to be
demanding heat - but once it is going, it keeps going when you turn down the
stat. This sounds like confused relay logic to me - with something staying
latched once energised.

--
Cheers,
Set Square
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If all else fails, replace this black box with a conventional CH junction
box in order to connect the programmer, boiler, pump and room stat in the
normal way. As I said before, you won't then be able to use the cyl stat -
unless you add a zone valve and convert it to a C-Plan system.

It is easy enough to use the cylinder stat without the zone valve, even
though it doesn't provide temperature limiting when in CH mode. The HW On
signal is just filtered through the cylinder stat before it goes on to turn
the boiler on.

Christian.

In an earlier contribution to this discussion,
Christian McArdle wrote:

If all else fails, replace this black box with a conventional CH
junction box in order to connect the programmer, boiler, pump and
room stat in the normal way. As I said before, you won't then be
able to use the cyl stat - unless you add a zone valve and convert
it to a C-Plan system.

It is easy enough to use the cylinder stat without the zone valve,
even though it doesn't provide temperature limiting when in CH mode.
The HW On signal is just filtered through the cylinder stat before it
goes on to turn the boiler on.

Christian.

In that case, you'd need a separate wire from the CH feed to the boiler -
rather than the usual internal strap which brings on HW when CH is selected.

No, hang on, you'd also need a relay. Otherwise, turning the boiler on for
HW would also bring on the CH!
--
Cheers,
Set Square
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No, hang on, you'd also need a relay. Otherwise, turning the boiler on for
HW would also bring on the CH!

There's all sorts of variations. Some need relays, some don't. However, you
don't need to install zone valves to get 80% of the benefit of the cylinder
stat.

Christian.

In an earlier contribution to this discussion,
Christian McArdle wrote:

No, hang on, you'd also need a relay. Otherwise, turning the boiler
on for HW would also bring on the CH!

There's all sorts of variations. Some need relays, some don't.
However, you don't need to install zone valves to get 80% of the
benefit of the cylinder stat.

Christian.

OK, I think I can see a way of doing it without either zone valve or relay.

How does this grab you?
* CH feed from programmer connected via room stat to pump
* Link in programmer to force HW on when CH on
* Cyl stat of changeover type, with Common connected to boiler
* NC connected to HW feed from programmer
* NO cross-connected to room stat output/pump

That should only fire the boiler when either or both stats require heat, and
only run the pump when CH (room) stat requires heat. Like other systems
without zone valves (or dual pumps) it won't stop the HW getting hotter than
required when the CH is on.

As you say, you probably get 80% of a zoned system benefit.
--
Cheers,
Set Square
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* CH feed from programmer connected via room stat to pump
* Link in programmer to force HW on when CH on
* Cyl stat of changeover type, with Common connected to boiler
* NC connected to HW feed from programmer
* NO cross-connected to room stat output/pump

Sounds good to me, unless I'm having a brainfart.

Christian.

On Mon, 26 Jul 2004 14:57:50 +0100, "Christian McArdle"
wrote:

* CH feed from programmer connected via room stat to pump
* Link in programmer to force HW on when CH on
* Cyl stat of changeover type, with Common connected to boiler
* NC connected to HW feed from programmer
* NO cross-connected to room stat output/pump

Sounds good to me, unless I'm having a brainfart.

Christian.

Jeez....you lost me a few posts back with the zone valve talk...

Well, I swtiched on the HW tonight (without the CH) and hey presto the
boiler fired up. Slightly incredulous, I switched it off then tried it
again - no luck this time. Does this sound consistent with a dodgy
relay?

In an earlier contribution to this discussion, ITM
wrote:

Well, I swtiched on the HW tonight (without the CH) and hey presto the
boiler fired up. Slightly incredulous, I switched it off then tried it
again - no luck this time. Does this sound consistent with a dodgy
relay?

Could be! Can you run it without the cover on the control box? Do the relays
click when you turn things on and off? Have you tried re-seating or swapping
them, as suggested before?

--
Cheers,
Set Square

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
ITM wrote:

The problem is that the
heating won't fire up the boiler unless the thermostat is turned up -
not great in the middle of summer, as I have a couple of bathroom
radiators which I can't turn off!

It gets mysteriouser!


Thanks for the explanation - makes perfect sense. Would the lack of a
motorised valve suggest that I have a gravity HW system?

Yes it would - but I'm puzzled as to what the cylinder stat does - 'cos
you
don't usually have one unless there is a motorised valve. Also the fact
that
the boiler keeps going when the pump stops suggests that it *isn't * fully
pumped - which again suggests gravity hot water.

The big question is: why can't I get the boiler started by switching
on just the hot water any more. My guess is that the electrics in the
"Fuel Guardian" box may have developed a fault, but I really wouldn't
know how to start investigating.


I can't say I've met a "Fuel Guardian" box by that name but they used to
have a variety of contemporaries a number of years ago. Basically they all
had the property of delaying the burn after the demand came on. Some were
more sophisticated than others and could start up from cold without the
delay but begin to delay once the temperature had risen a predetermined
amount.
At a guess the Fuel Guardian fits the slightly sophisticated version and its
likely that the hot water demand isn't resulting in energisation of the gas
valve. I still come across these sort of boxes in boilerhouses but almost
without exception they are either switched to bypass or disconnected and
bridged out. I'd suggest yours may be a candidate for the same treatment if
the company has gone bust. (Of course Geoff at CET may be able to repair it
for you)

On Mon, 26 Jul 2004 21:09:01 +0100, "Set Square"
wrote:

Well, I swtiched on the HW tonight (without the CH) and hey presto the
boiler fired up. Slightly incredulous, I switched it off then tried it
again - no luck this time. Does this sound consistent with a dodgy
relay?

Could be! Can you run it without the cover on the control box? Do the relays
click when you turn things on and off? Have you tried re-seating or swapping
them, as suggested before?

The relay clicks and the "boiler" LED lights up when I switch the HW
on, but the boiler doesn't fire up (well, not most of the time
anyway).

On Mon, 26 Jul 2004 21:20:49 +0000 (UTC), "John"
wrote:

I can't say I've met a "Fuel Guardian" box by that name but they used to
have a variety of contemporaries a number of years ago. Basically they all
had the property of delaying the burn after the demand came on. Some were
more sophisticated than others and could start up from cold without the
delay but begin to delay once the temperature had risen a predetermined
amount.
At a guess the Fuel Guardian fits the slightly sophisticated version and its
likely that the hot water demand isn't resulting in energisation of the gas
valve. I still come across these sort of boxes in boilerhouses but almost
without exception they are either switched to bypass or disconnected and
bridged out. I'd suggest yours may be a candidate for the same treatment if
the company has gone bust. (Of course Geoff at CET may be able to repair it
for you)

Interesting - I've just tried switching the Hot Water switch on the
Fuel Guardian from "Auto" to "Override", and now the boiler fires up
whenever I switch the HW on. I can't believe that I didn't try this
before - maybe I'm losing my mind.

If this box simply delays the burn after the demand comes in, is there
any harm in overriding it? What's the benefit of this delay?

In an earlier contribution to this discussion, ITM
wrote:
On Mon, 26 Jul 2004 21:09:01 +0100, "Set Square"
wrote:

Well, I swtiched on the HW tonight (without the CH) and hey presto
the boiler fired up. Slightly incredulous, I switched it off then
tried it again - no luck this time. Does this sound consistent with
a dodgy relay?

Could be! Can you run it without the cover on the control box? Do
the relays click when you turn things on and off? Have you tried
re-seating or swapping them, as suggested before?

The relay clicks and the "boiler" LED lights up when I switch the HW
on, but the boiler doesn't fire up (well, not most of the time
anyway).

Sounds like the relay is energising but the contacts are shot then. Does the
relay unplug from a socket, or is it soldered in? Is there any
identification on it?
--
Cheers,
Set Square

On Mon, 26 Jul 2004 21:43:37 GMT, ITM wrote:

Interesting - I've just tried switching the Hot Water switch on the
Fuel Guardian from "Auto" to "Override", and now the boiler fires up
whenever I switch the HW on. I can't believe that I didn't try this
before - maybe I'm losing my mind.

It looks like this isn't a solution after all - the boiler switches
back to pilot after a few minutes - i.e. long before the tank is hot.
The "Boiler" light on the Fuel Guardian stays on, though.
Only switching the heating on will keep the HW running long enough to
heat the tank.

"ITM" wrote in message
...
On Mon, 26 Jul 2004 21:43:37 GMT, ITM wrote:

Interesting - I've just tried switching the Hot Water switch on the
Fuel Guardian from "Auto" to "Override", and now the boiler fires up
whenever I switch the HW on. I can't believe that I didn't try this
before - maybe I'm losing my mind.

It looks like this isn't a solution after all - the boiler switches
back to pilot after a few minutes - i.e. long before the tank is hot.
The "Boiler" light on the Fuel Guardian stays on, though.
Only switching the heating on will keep the HW running long enough to
heat the tank.

Turn up the thermostat on your boiler?

Perhaps it is the area of the problem.

Logic (possibly dodgy):

Boiler comes on HW only; gravity circulation is slow; boiler switches off
because it gets up to temperature and then doesn't switch back on again
because of thermostat fault (or other side effect of Fuel Guardian not
disabled by 'override' switch).

Boiler comes on for CH; pumped circulation keeps water temperature low until
radiators are warm, by which time water in cyclinder is hot.

Does the boiler cycle (i.e. switch on and off) whilst running in CH mode?

HTH
Dave R

P.S. Another passing thought - does the pump drive water around the HW
circuit when pumping the CH? If so there could be an obstruction (loose
scale etc.) in the HW circulation which is preventing it working properly on
gravity but which allows pressurised water from the pump to flow around.
This is not very likely IMHO but may be a possibility.

"ITM" wrote in message
...
On Mon, 26 Jul 2004 21:20:49 +0000 (UTC), "John"
wrote:

I can't say I've met a "Fuel Guardian" box by that name but they used to
have a variety of contemporaries a number of years ago. Basically they
all
had the property of delaying the burn after the demand came on. Some were
more sophisticated than others and could start up from cold without the
delay but begin to delay once the temperature had risen a predetermined
amount.
At a guess the Fuel Guardian fits the slightly sophisticated version and
its
likely that the hot water demand isn't resulting in energisation of the
gas
valve. I still come across these sort of boxes in boilerhouses but almost
without exception they are either switched to bypass or disconnected and
bridged out. I'd suggest yours may be a candidate for the same treatment
if
the company has gone bust. (Of course Geoff at CET may be able to repair
it
for you)

Interesting - I've just tried switching the Hot Water switch on the
Fuel Guardian from "Auto" to "Override", and now the boiler fires up
whenever I switch the HW on. I can't believe that I didn't try this
before - maybe I'm losing my mind.

If this box simply delays the burn after the demand comes in, is there
any harm in overriding it? What's the benefit of this delay?

It was claimed that by delaying the burn it reduced gas/oil usage
(anti-cycling device). Problem was that it simply deferred the burn and it
consequently burnt after it would have normally shut down anyway hence
overall the savings by no means paid for the outlay :-(
No-one ever wanted to explore what the extra cooling and heating
contraction/expansion would cost in the grand scale of things so IMHO there
wasn't much point in adding these to a working system (except perhaps to
line the pockets of the marketing organisation)

"ITM" wrote in message ...

[Fuel Guardian, etc.]
If this box simply delays the burn after the demand comes in, is
there any harm in overriding it? What's the benefit of this delay?

The main benefit of these boxes is that they made money for their vendors;
they were a well known scam in the 80s, about as useful as, dare I say it,
magnetic or electronic water conditioners. They'll save fuel in an old
gravity system with no cylinder 'stat where the boiler is allowed to cycle
endlessly on no load. By ensuring that the 'monitoring trial' was carried
out under those conditions the vendors were able to demonstrate impressive
potential savings. With proper modern controls all they do is reduce the
performance of your system. Out with it!

--
Andy

"Andy Wade" wrote in message
...
"ITM" wrote in message ...

[Fuel Guardian, etc.]
If this box simply delays the burn after the demand comes in, is
there any harm in overriding it? What's the benefit of this delay?

The main benefit of these boxes is that they made money for their vendors;
they were a well known scam in the 80s, about as useful as, dare I say it,
magnetic or electronic water conditioners.

My electronic water descaler works.