My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

b) a failing gas valve (replacement where from) or

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

The boiler is still producing some heat but it is struggling to get the
house up to temperature while it is relatively warm outside. Something
could of course fail permanently at any time and no doubt there is
another cold spell round the corner when the boiler just won't be able
to cope in its present state.

--
Roger Chapman

On Jan 25, 10:31*am, Roger wrote:
My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

b) a failing gas valve (replacement where from) or

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

The boiler is still producing some heat but it is struggling to get the
house up to temperature while it is relatively warm outside. Something
could of course fail permanently at any time and no doubt there is
another cold spell round the corner when the boiler just won't be able
to cope in its present state.

--
Roger Chapman

Usually it's something like this.. controls call for heating or
whatever, pcb says ok open gas valve and light the pilot. The
thermocouple then tells it yep the pilot is lit so it starts the fan.
The fan sensor then says yep the fan is working go ahead and open the
main gas valve. If the temp gets too hot then the boiler thermostat
tells it to switch off. if it gets really really hot then the
overheat stat cuts in. So you need to check all the sensors valves
etc in order and work out which is flaky :-)

The message

from adder1969 contains these words:

Usually it's something like this.. controls call for heating or
whatever, pcb says ok open gas valve and light the pilot. The
thermocouple then tells it yep the pilot is lit so it starts the fan.
The fan sensor then says yep the fan is working go ahead and open the
main gas valve. If the temp gets too hot then the boiler thermostat
tells it to switch off. if it gets really really hot then the
overheat stat cuts in. So you need to check all the sensors valves
etc in order and work out which is flaky :-)

Thanks for that

The way I see it none of the sensors other than the thermocouple are
seeing heat at that stage as the problem is there at start up. So how do
I check for a flaky themocouple short of just fitting a new one?

--
Roger Chapman

On Fri, 25 Jan 2008 10:31:03 +0000, Roger wrote:

My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

b) a failing gas valve (replacement where from) or

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

The boiler is still producing some heat but it is struggling to get the
house up to temperature while it is relatively warm outside. Something
could of course fail permanently at any time and no doubt there is
another cold spell round the corner when the boiler just won't be able
to cope in its present state.

Roger, seriously, let's start over on this one.
There is no thermocouple on this boiler.

The black control box (available from cetltd) runs everything.

IME the most common fault on the box is that the internal relay does not
acknowledge the APS. This causes the fan to stop and start repeatedly.
This is not the case for you as if you have ANY flames the fan/APS and
controls are good.

The box open the pilot gas valve and begins sparking. If you have ANY
flames then you must have got this far. The same HT lead that lit the
flames now sense that the pilot flame is good, and the box opens the main
gas valve.

The problem looks like its in flame detection and/or reliable flame
detection.

1) Service or get the boiler serviced. Make sure that all the part are
free of crap and the HT lead is in good order and making good contact at
both ends. The mains electric supply is round the right way and the earth
is good.

2) If that fails to harden or remove the fault then replace the HT lead.

3) If you see the main flames even if only for a second then we know the
gas valve is OK. The gas valve is easy to condemn/clear based on it's
supply voltage.

4) If everything appears to be OK then replace the black box.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

In message
,
adder1969 writes
On Jan 25, 10:31*am, Roger wrote:
My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

b) a failing gas valve (replacement where from) or

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

The boiler is still producing some heat but it is struggling to get the
house up to temperature while it is relatively warm outside. Something
could of course fail permanently at any time and no doubt there is
another cold spell round the corner when the boiler just won't be able
to cope in its present state.

--
Roger Chapman

Usually it's something like this.. controls call for heating or
whatever, pcb says ok open gas valve and light the pilot. The
thermocouple then tells it yep the pilot is lit so it starts the fan.
The fan sensor then says yep the fan is working go ahead and open the
main gas valve.

Sorry, but that's total ********

A call for heat powers up the pcb which, if the stat (white wires)
presents a short circuit, brings on the fan, which transfers the air
pressure switch from normally closed to normally open. This feeds back
to the pcb which a) opens the pilot valve and b) powers the spark
circuit. When the pilot flame is established, the pcb senses the flame
by electronic means (there is no thermocouple), and opens the main gas
valve.




--
geoff

In message , Roger
writes
My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

there is no thermocouple


b) a failing gas valve (replacement where from) or

could be - or faulty overheat stat, or reduced circulation for some
reason

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

No, I don't think it's likely to be the pcb, if the boiler dies with a
reasonably reliable time period

John or Ed are the people to ask here


--
geoff

On 25 Jan, 19:29, geoff wrote:
In message , Roger
writes

My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

there is no thermocouple



b) a failing gas valve (replacement where from) or

could be - or faulty overheat stat, or reduced circulation for some
reason



c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

No, I don't think it's likely to be the pcb, if the boiler dies with a
reasonably reliable time period

John or Ed are the people to ask here

--
geoff

Just a thought. I once (and only once) came across a gas valve with a
gauze at the inlet. Said gauze was semi-clogged with dust from inside
the gas pipe and when the main falme lit up it starved the pilot which
became unstable and sporadically the flame sense failed. Does the
flame "look" ok during this problem?

The message
from geoff contains these words:

No, I don't think it's likely to be the pcb, if the boiler dies with a
reasonably reliable time period

John or Ed are the people to ask here

Thanks.

--
Roger Chapman

The message
from Ed Sirett contains these words:

Thanks for the advice Ed.

Roger, seriously, let's start over on this one.
There is no thermocouple on this boiler.

Whoops! I suppose I must have known that once since I installed the
boiler in the first place and have since repaired it.

The black control box (available from cetltd) runs everything.

IME the most common fault on the box is that the internal relay does not
acknowledge the APS. This causes the fan to stop and start repeatedly.
This is not the case for you as if you have ANY flames the fan/APS and
controls are good.

The box open the pilot gas valve and begins sparking. If you have ANY
flames then you must have got this far. The same HT lead that lit the
flames now sense that the pilot flame is good, and the box opens the main
gas valve.

The problem looks like its in flame detection and/or reliable flame
detection.

I did think the spark was looking a bit feeble. I have in the past had
to close the gap up (by brute force there being no means of adjustment).
Could a borderline spark gap be responsible?

1) Service or get the boiler serviced. Make sure that all the part are
free of crap and the HT lead is in good order and making good contact at
both ends. The mains electric supply is round the right way and the earth
is good.

2) If that fails to harden or remove the fault then replace the HT lead.

The fan and the HT lead have both been replaced in recent years.

3) If you see the main flames even if only for a second then we know the
gas valve is OK. The gas valve is easy to condemn/clear based on it's
supply voltage.

I will try that if reducing the spark gap doesn't make a difference.

4) If everything appears to be OK then replace the black box.

I hope it doesn't come to that although Geoffs prices won't break the bank.

On Fri, 25 Jan 2008 18:45:26 +0000, Ed Sirett wrote:

The problem looks like its in flame detection and/or reliable flame
detection.

I had one recently where it sometimes would stick at pilot light on, no
sparking (so flame sense OK) but would not pass Go or collect £200 ... or
fire up the main burner. Turned out to be a dodgy solder joint between the
Molex and the PCB. (Thanks for the telephone consultation Geoff and John
at CET!)

--
John Stumbles

Who's *really* behind all these conspiracy theories?

The message
from cynic contains these words:

Just a thought. I once (and only once) came across a gas valve with a
gauze at the inlet. Said gauze was semi-clogged with dust from inside
the gas pipe and when the main falme lit up it starved the pilot which
became unstable and sporadically the flame sense failed. Does the
flame "look" ok during this problem?

It looks ok colourwise (well perhaps a tinge of yellow) but something is
turning the gas supply off in relatively short order.

--
Roger Chapman

The message
from Roger contains these words:

The problem looks like its in flame detection and/or reliable flame
detection.

I did think the spark was looking a bit feeble.

Well I have closed the spark gap down to the minimum (2.5 mm) and the
spark looks ok but it hasn't made a blind bit of difference to my
problem.

I will have to leave the detective work to another day which may not be
as soon as tomorrow unless the problem gets worse as I have an urgent
appointment with my boundary wall. I discovered today that a 15 foot
section of the wall had collapsed into a narrow public path completely
blocking it and as yet I haven't finished removing the rubble. It is a
dry stone wall so will go up again once I have dug down and relaid the
foundation stones but at 6 feet high there is a lot of stone to play
with and only a couple of days of fine (ish) weather in prospect.

--
Roger Chapman

In message , Roger
writes
The message
from cynic contains these words:

Just a thought. I once (and only once) came across a gas valve with a
gauze at the inlet. Said gauze was semi-clogged with dust from inside
the gas pipe and when the main falme lit up it starved the pilot which
became unstable and sporadically the flame sense failed. Does the
flame "look" ok during this problem?

It looks ok colourwise (well perhaps a tinge of yellow) but something is
turning the gas supply off in relatively short order.

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?


--
geoff

The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

Not yet, nor even established where I can get probes in. ISTR that last
time I ferreted about in the boiler electrics I had trouble with
shrouded connectors.

The house was up to temperature when I got up so I am not sure whether
the boiler was misbehaving this morning.

They do say that troubles come in threes and to add to the boiler and
boundary wall problems I now have a domestic hot water leak. There is a
puddle partly under the washing machine machine but luckily the source
was a drip from above so I just have to tear up the bathroom floor
rather than tear the washing machine apart.

--
Roger Chapman

In article ,
Roger writes:
My elderly boiler is having ignition problems.

The symptoms are that it fires up normally but over the next 10 or so
seconds the gas flame starts to flicker and then goes out. Depending on
whether or not the pilot light goes out as well (it varies) there is a
delay before the sequence is repeated. Is the most likely problem:

a) A failing thermocouple, (which I can presumably source locally)

b) a failing gas valve (replacement where from) or

c) a failing control board (which needs replacing with a reconditioned
one from Geoff)

If the flame dies down gradually, I doubt that's the boiler
as it has no modulation control of the gas valve; sounds like
a lack of gas. Have you got a gas hob, and if so does a lit
gas burner do the same thing at the same time? If so, check
the main gas cock is fully open, and if it is, sounds like
the main regulator has died.

OTOH, if you can hear the gas valve operating simultaneously
as the flames die, then it's not this.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

I have now checked the gas valve.

Apart from the earth there are 3 wires, black, blue and white. I assume
that black/blue is the 240V supply and white is the control wire.

When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.

--
Roger Chapman

In message , Roger
writes
The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

Not yet, nor even established where I can get probes in.

You should be able to get them into the molex connector on the pcb (pins
1 & 3 from the top I think)

--
geoff

In message , Roger
writes
The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

I have now checked the gas valve.

Apart from the earth there are 3 wires, black, blue and white. I assume
that black/blue is the 240V supply and white is the control wire.

main, pilot and common

There is a basic diagram on the pcb cover which should give you a clue



When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.





--
geoff

The message
from geoff contains these words:

In message , Roger
writes
The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

I have now checked the gas valve.

Apart from the earth there are 3 wires, black, blue and white. I assume
that black/blue is the 240V supply and white is the control wire.

main, pilot and common

There is a basic diagram on the pcb cover which should give you a clue

T1/T3 Gas Valve
T4/T5 Air pressure switch
T7/T8 Fan

Sorry but none the wiser.



When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.

So is the gas valve working properly or not?

--
Roger Chapman

In message , Roger
writes
The message
from geoff contains these words:

In message , Roger
writes
The message
from geoff contains these words:

Have you put a meter on the solenoid contacts to see if it is a gas
valve problem or it's losing it's power ?

I have now checked the gas valve.

Apart from the earth there are 3 wires, black, blue and white. I assume
that black/blue is the 240V supply and white is the control wire.

main, pilot and common

There is a basic diagram on the pcb cover which should give you a clue

T1/T3 Gas Valve
T4/T5 Air pressure switch
T7/T8 Fan

Sorry but none the wiser.



When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.

So is the gas valve working properly or not?


I think it's T1 - T3 = main valve

T2 - T3 = pilot valve
--
geoff

The message
from geoff contains these words:

There is a basic diagram on the pcb cover which should give you a clue

T1/T3 Gas Valve
T4/T5 Air pressure switch
T7/T8 Fan

Sorry but none the wiser.



When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.

So is the gas valve working properly or not?


I think it's T1 - T3 = main valve

T2 - T3 = pilot valve

Sorry, I should have made it clearer. I have the Installation and
Servicing Instructions so I know which connections are which (if I think
to look at the right diagram) but my problem is more basic than that - I
am having trouble work out for sure what I should expect to see on a
meter at each stage of the process. Which process is not being helped by
the fact that I seem to have recorded volts on white the wrong way round
when looking at the boiler last night.

T1 is white and goes to GV2.
T2 is black and goes to GV1.
T3 is blue and is common to GV1 and GV2.

When calling for heat volts present all the time across T2/T3 so is that
the pilot light valve which remains lit during main firing?

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

But where and what do I look for?

--
Roger Chapman

On Sun, 27 Jan 2008 09:15:38 +0000, Roger wrote:

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

Yup, if you're losing voltage acorss the main valve then you need to look
further upstream, on the PCB itself. As I said earlier I had one recently
with a bad solder joint on the PCB to the Molex connector. However the PCB
will drop the main valve if it doesn't sense a flame so watch and listen
(for a quiet 'tick' about 1-2 a second) to see if it's sparking to try to
re-light the pilot.



--
John Stumbles

Xenophobia? Sounds a bit foreign to me.

In message , John Stumbles
writes
On Sun, 27 Jan 2008 09:15:38 +0000, Roger wrote:

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

Yup, if you're losing voltage acorss the main valve then you need to look
further upstream, on the PCB itself. As I said earlier I had one recently
with a bad solder joint on the PCB to the Molex connector. However the PCB
will drop the main valve if it doesn't sense a flame so watch and listen
(for a quiet 'tick' about 1-2 a second) to see if it's sparking to try to
re-light the pilot.

Does the fan go out ?

it could be the overheat turning it off


--
geoff

In message , Roger
writes
The message
from geoff contains these words:

There is a basic diagram on the pcb cover which should give you a clue

T1/T3 Gas Valve
T4/T5 Air pressure switch
T7/T8 Fan

Sorry but none the wiser.



When calling for heat there is 240V across black/blue whether the boiler
is firing or not.

While the boiler is firing there are no volts on white. When it is not
firing there are 240V on white.

So is the gas valve working properly or not?


I think it's T1 - T3 = main valve

T2 - T3 = pilot valve

Sorry, I should have made it clearer. I have the Installation and
Servicing Instructions so I know which connections are which (if I think
to look at the right diagram) but my problem is more basic than that - I
am having trouble work out for sure what I should expect to see on a
meter at each stage of the process. Which process is not being helped by
the fact that I seem to have recorded volts on white the wrong way round
when looking at the boiler last night.

T1 is white and goes to GV2.
T2 is black and goes to GV1.
T3 is blue and is common to GV1 and GV2.

When calling for heat volts present all the time across T2/T3 so is that
the pilot light valve which remains lit during main firing?

While it's sparking, you expect to see volts across T2/T3, that's the
pilot valve

Once the sparking stops, the pcb has sensed that the pilot is alight and
opens the main valve which is across T1/T3

T2/T3 remains energised


When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

But where and what do I look for?


--
geoff

On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

--
John Stumbles

What do you mean, talking about it isn't oral sex?

The message
from geoff contains these words:

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

Yup, if you're losing voltage acorss the main valve then you need to look
further upstream, on the PCB itself. As I said earlier I had one recently
with a bad solder joint on the PCB to the Molex connector. However the PCB
will drop the main valve if it doesn't sense a flame so watch and listen
(for a quiet 'tick' about 1-2 a second) to see if it's sparking to try to
re-light the pilot.

Does the fan go out ?

it could be the overheat turning it off

Not as far as I am aware but I have yet to establish a foolproof way of
checking it is running.

--
Roger Chapman

The message
from John Stumbles contains these words:

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

Yup, if you're losing voltage acorss the main valve then you need to look
further upstream, on the PCB itself. As I said earlier I had one recently
with a bad solder joint on the PCB to the Molex connector. However the PCB
will drop the main valve if it doesn't sense a flame so watch and listen
(for a quiet 'tick' about 1-2 a second) to see if it's sparking to try to
re-light the pilot.

Can't guarantee that it is always the case but sometimes the pilot flame
has stayed lit and sometimes it has gone out between attempts to light
the main burner and at least some of the times it has gone out the spark
has been visible almost immediately.

I don't actually know what a Molex connector is but if it does come down
to a bad solder joint then I don't think I could remake it sucessfully.
(Now if only it was a matter of hitting it with a big hammer :-().

However the boiler is currently behaving itself so I will have to wait
awhile before I can do any more checking.

--
Roger Chapman

On Sun, 27 Jan 2008 14:37:48 +0000, John Stumbles wrote:

On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

Furthermore the O/H cut out on this boiler is way upstream. IIRC it
breaks all power to the boiler you get absolutely nothing at all until
you have found the brown recessed button underneath and pressed it in.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

"Ed Sirett" wrote in message
...
On Sun, 27 Jan 2008 14:37:48 +0000, John Stumbles wrote:

On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

Furthermore the O/H cut out on this boiler is way upstream. IIRC it
breaks all power to the boiler you get absolutely nothing at all until
you have found the brown recessed button underneath and pressed it in.

It also forces the pump on to keep the water flowing through the boiler.

/john

In message , Ed Sirett
writes
On Sun, 27 Jan 2008 14:37:48 +0000, John Stumbles wrote:

On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

Furthermore the O/H cut out on this boiler is way upstream. IIRC it
breaks all power to the boiler you get absolutely nothing at all until
you have found the brown recessed button underneath and pressed it in.

Re. your IIRC - that is exactly what the P.Profile here does. It
happened about a month ago and, having pressed the recessed button
(can't see what colour it is), the boiler has been running fine since.
Is there anything I should be concerned about if this happens
occasionally?

--
Si

In message , John Kenyon
writes

"Ed Sirett" wrote in message
...
On Sun, 27 Jan 2008 14:37:48 +0000, John Stumbles wrote:

On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

Furthermore the O/H cut out on this boiler is way upstream. IIRC it
breaks all power to the boiler you get absolutely nothing at all until
you have found the brown recessed button underneath and pressed it in.

It also forces the pump on to keep the water flowing through the boiler.

Not forever though. Until the boiler has cooled to an acceptable
temperature?

--
Si

In message , John Stumbles
writes
On Sun, 27 Jan 2008 12:49:54 +0000, geoff wrote:

Does the fan go out ?

it could be the overheat turning it off

yebbut he said the pilot only goes out sometimes.

I'm just checking, since, without flame sense problems, it's a rare
(pcb) fault and I can't offhand think of an obvious reason for a
reliable and regular main valve drop out


--
geoff

On Sun, 27 Jan 2008 18:29:18 +0000, Si wrote:

Is there anything I should be concerned about if this happens
occasionally?

If it happens often enough to motivate you to track down the problem you
need to check how hot the flow pipe is getting when the cutout cuts out.
An IR thermometer is useful for this (with a bit of plack insulating tape
stuck on the pipe to give a good reading). If the temperature is OK but
the cutout trips replace it. If the temperature really is getting sky high
you probably need to check the boiler thermostat.


--
John Stumbles

Seagull Management
Management technique characterised by flying in, making a lot of noise,
crapping on everything, and then leaving.

In message , John Stumbles
writes
On Sun, 27 Jan 2008 18:29:18 +0000, Si wrote:

Is there anything I should be concerned about if this happens
occasionally?

If it happens often enough to motivate you to track down the problem you
need to check how hot the flow pipe is getting when the cutout cuts out.
An IR thermometer is useful for this (with a bit of plack insulating tape
stuck on the pipe to give a good reading).

(I have both of these due to recent threads herein.

If the temperature is OK but
the cutout trips replace it. If the temperature really is getting sky high
you probably need to check the boiler thermostat.

Thanks John. Tomorrow I'll take a reading of the pipe where it exits the
boiler to get a baseline reading.

--
Si

The message
from geoff contains these words:

I'm just checking, since, without flame sense problems, it's a rare
(pcb) fault and I can't offhand think of an obvious reason for a
reliable and regular main valve drop out

It has become an intermittent problem, and, thinking about it, it may
have been around at a low level for some considerable time. What
triggered my concern was getting up to a house that was 2 degrees short
of being up to temperature, and that after a relatively warm night.

Is there any chance that the ignition lead (which is relatively new) is
good enough to transmit the spark but not good enough to always pass the
flame detection current (assuming that is the way it works)?

I happening to enter the kitchen (to prepare my tea) just before the
room stat decided to call for heat. The on-off start-up procedure went
through about 3 cycles before I abandoned food preparation and moved to
the boiler. Having wasted a few cycles checking the obvious I set about
watching both the volts on the main valve and the burner flame to see if
the flicker in the flame that precedes cut-off was reflected in the
voltage but the boiler had other ideas and I soon got fed up of waiting
for a sign. After several minutes there was another hic-up, but just the
one, so I had missed the chance to do some more checking.

--
Roger Chapman

In message , Roger
writes
The message
from geoff contains these words:

I'm just checking, since, without flame sense problems, it's a rare
(pcb) fault and I can't offhand think of an obvious reason for a
reliable and regular main valve drop out

It has become an intermittent problem, and, thinking about it, it may
have been around at a low level for some considerable time. What
triggered my concern was getting up to a house that was 2 degrees short
of being up to temperature, and that after a relatively warm night.

Is there any chance that the ignition lead (which is relatively new) is
good enough to transmit the spark but not good enough to always pass the
flame detection current (assuming that is the way it works)?

IF the HT lead is faulty and doesn't flame sense, then you would hear it
sparking again to try and ignite the pilot (which the pcb doesn't think
is alight because ...)

--
geoff

In message , Roger
writes
The message
from John Stumbles contains these words:

When the main burner is firing there are volts on T1/T3 and loss of
volts turns the main burner out so is the gas valve is OK and I need to
look elsewhere for the fault?

Yup, if you're losing voltage acorss the main valve then you need to look
further upstream, on the PCB itself. As I said earlier I had one recently
with a bad solder joint on the PCB to the Molex connector. However the PCB
will drop the main valve if it doesn't sense a flame so watch and listen
(for a quiet 'tick' about 1-2 a second) to see if it's sparking to try to
re-light the pilot.

Can't guarantee that it is always the case but sometimes the pilot flame
has stayed lit and sometimes it has gone out between attempts to light
the main burner and at least some of the times it has gone out the spark
has been visible almost immediately.

I don't actually know what a Molex connector is but if it does come down
to a bad solder joint then I don't think I could remake it sucessfully.
(Now if only it was a matter of hitting it with a big hammer :-().

However the boiler is currently behaving itself so I will have to wait
awhile before I can do any more checking.

You might be just as well having a pcb from me and then you know that
you've eliminated the electronics ...

although I'm not convinced that the fault lies there

--
geoff

The message
from geoff contains these words:

You might be just as well having a pcb from me and then you know that
you've eliminated the electronics ...

although I'm not convinced that the fault lies there

You may be right. Expect a telephone call from me sometime this week.

Will I need a new ignition lead? It is relatively new but the original
started shedding insulation when I disturbed it during a routine
service. And if so where from? In the past I have gone to HRPC but they
charge an arm and a leg.

--
Roger Chapman

On Mon, 28 Jan 2008 09:39:46 +0000, Roger wrote:

The message from geoff
contains these words:

You might be just as well having a pcb from me and then you know that
you've eliminated the electronics ...

although I'm not convinced that the fault lies there

You may be right. Expect a telephone call from me sometime this week.

Will I need a new ignition lead? It is relatively new but the original
started shedding insulation when I disturbed it during a routine
service. And if so where from? In the past I have gone to HRPC but they
charge an arm and a leg.

it sounds like there may be a reason why the pilot sometimes drops out
(dirt around pilot burner or pilot injector). It might even be that the
pilot flame needs adjusting (screw on gas valve for this, IIRC).

Should the flame die or move away from the spark electrode then the main
GV will be killed in short order. The PCB is fairly basic and as soon as
the the flame failure has occurred the spark generator will try to light
the pilot again.

If the pilot flame/flame sensing was marginal then it's possible the
boiler would effectively be operating on about a 50% duty cycle. Likely
less than 50% of rated output aswell.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

In message , Roger
writes
The message
from geoff contains these words:

You might be just as well having a pcb from me and then you know that
you've eliminated the electronics ...

although I'm not convinced that the fault lies there

You may be right. Expect a telephone call from me sometime this week.

Will I need a new ignition lead? It is relatively new but the original
started shedding insulation when I disturbed it during a routine
service.

impossible to tell without seeing it

And if so where from?

Local CH merchant ?

In the past I have gone to HRPC but they
charge an arm and a leg.


--
geoff