On Monday, 9 January 2017 17:05:36 UTC, Grumps wrote:
On 09/01/2017 16:51, charles wrote:
In article ,
Grumps wrote:
Happy New Year etc.
Brexit, Daesh, Trump etc, blah blah, but more importantly my boiler is
having issues.

No hot water this morning and it was evident that the boiler (a 30 year
old Potterton) was off.
It restarted OK and ran for a few minutes.

I changed the thermocouple but it behaves the same.
In fact, if it's just the pilot that is on, then it stays on. It's only
when the burners start that it shuts down after about 2-3 minutes.

Any ideas or is it time to call a man in?
Ta.

Mine - of similar vintage (1988) but not Potterton - suffered a similar
problem a few years go and it was found (not by me) to be a faulty overheat
sensor. It was simply bypassed until a new one was fitted.

So when your overheat sensor triggered it shut down the whole boiler,
pilot and all?
How do they work? If I disconnect it will the boiler work or stay in
shutdown?
I see what looks like another thermocouple lead going to the top of the
boiler.

A metal bulb containing liquid expands when heated, pushing itself down the capillary tube and opening the switch.


NT

On 09/01/2017 20:32, Grumps wrote:

Its last service was in 2011.
The main burner flames look good to me.


What colour is the main burner flame? Mainly blue? Mainly yellow/orange?

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charles wrote:
In article ,
Tim+ wrote:
Grumps wrote:
On 09/01/2017 14:23, Grumps wrote:
Happy New Year etc.
Brexit, Daesh, Trump etc, blah blah, but more importantly my boiler is
having issues.

No hot water this morning and it was evident that the boiler (a 30 year
old Potterton) was off.
It restarted OK and ran for a few minutes.

I changed the thermocouple but it behaves the same.
In fact, if it's just the pilot that is on, then it stays on. It's only
when the burners start that it shuts down after about 2-3 minutes.

Any ideas or is it time to call a man in?
Ta.

Update:
Gas man has visited and cleaned out the burner and pilot jet. So much
crud came out.
The pilot was cleaned as much as possible and its supply pipe tightened
and sealed to remove the leak that was there.
The pilot flame is now much stronger and still touches the thermocouple
when the main burner starts.
The old boiler has been running for an hour, so all seems well.

Thanks to all for your comments.



Glad you're up and running again. Don't neglect the servicing for so long
again though. Open vented boilers can fill your house with carbon monoxide
if not operating properly.

That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim

--
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On 10/01/2017 23:25, Tim+ wrote:

wrote:


That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim



It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.
--
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Roger
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In article ,
Roger Mills wrote:
On 10/01/2017 23:25, Tim+ wrote:

wrote:


That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim



It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.

Only if the boiler isn't room sealed - and it seems his is.

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

On 11/01/2017 13:32, Dave Plowman (News) wrote:
In ,
Roger wrote:
On 10/01/2017 23:25, Tim+ wrote:

wrote:


That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim



It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.

Only if the boiler isn't room sealed - and it seems his is.


You can still get CO from a room-sealed boiler if the casing seals are
not intact.
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Roger
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In article ,
Roger Mills wrote:
It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.

Only if the boiler isn't room sealed - and it seems his is.


You can still get CO from a room-sealed boiler if the casing seals are
not intact.

You can get an explosion if you have a gas leak too.
Don't use any boiler with faults.

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

On 11/01/2017 13:32, Dave Plowman (News) wrote:
In article ,
Roger Mills wrote:
On 10/01/2017 23:25, Tim+ wrote:

wrote:


That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim



It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.

Only if the boiler isn't room sealed - and it seems his is.

Yep, room sealed boiler, and I also have a CO alarm.

On 10/01/2017 23:09, alan_m wrote:
On 09/01/2017 20:32, Grumps wrote:

Its last service was in 2011.
The main burner flames look good to me.


What colour is the main burner flame? Mainly blue? Mainly yellow/orange?

Mainly blue. Can't see the top of the flame though.

On 11/01/2017 16:54, Roger Mills wrote:
On 11/01/2017 13:32, Dave Plowman (News) wrote:
In ,
Roger wrote:
On 10/01/2017 23:25, Tim+ wrote:

wrote:


That's why I have a CO monitor alarm close to by boiler


Lovely. How does that help Grumps? ;-)

Tim



It might encourage him to do likewise and rely on the monitor rather
than having the boiler serviced.

Only if the boiler isn't room sealed - and it seems his is.


You can still get CO from a room-sealed boiler if the casing seals are
not intact.

Which is why many modern designs run the case at negative pressure - so
if there is a leak it draws air in, rather than allows combustion
products out.

--
Cheers,

John.

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In article ,
Grumps wrote:
On 10/01/2017 23:09, alan_m wrote:
On 09/01/2017 20:32, Grumps wrote:

Its last service was in 2011.
The main burner flames look good to me.


What colour is the main burner flame? Mainly blue? Mainly yellow/orange?

Mainly blue. Can't see the top of the flame though.

When I had this problem, the flame on mine was a normal colour. Only very
small.

--
*Generally speaking, you aren't learning much if your lips are moving.*

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

On Wed, 11 Jan 2017 22:54:38 +0000, John Rumm wrote:

Which is why many modern designs run the case at negative pressure
- so if there is a leak it draws air in, rather than allows
combustion products out.

Can't see any mention of this on the Vaillant or Bosch sites?

On Monday, January 9, 2017 at 9:54:42 PM UTC, John Rumm wrote:
On 09/01/2017 20:04, Grumps wrote:
On 09/01/2017 18:49, John Rumm wrote:
On 09/01/2017 16:39, Grumps wrote:
On 09/01/2017 16:25, Clive Arthur wrote:
On 09/01/2017 16:09, Grumps wrote:
On 09/01/2017 15:29, Tim+ wrote:
Grumps wrote:
Happy New Year etc.
Brexit, Daesh, Trump etc, blah blah, but more importantly my
boiler is
having issues.

No hot water this morning and it was evident that the boiler (a 30
year
old Potterton) was off.
It restarted OK and ran for a few minutes.

I changed the thermocouple but it behaves the same.
In fact, if it's just the pilot that is on, then it stays on. It's
only
when the burners start that it shuts down after about 2-3 minutes.

Any ideas or is it time to call a man in?
Ta.


Is the pump running? Does it have an overheat stat that automatically
resets or is it one that you have to manually reset?

Tim

The pump runs (or sounds like it).
The overheat stat automatically resets.

This happened to my dad's boiler. The pump wasn't pumping, as Tim
hints, and the boiler was shutting down on overheat a few minutes after
firing up.

Before it shuts down, feel the pipes either side of the pump. If it's
pumping, they'll be much the same temperature. In my dad's case, there
was a clear difference in temperature, and a replacement pump
(ToolStation IIRC) fixed it.

(The 'heating engineer' dad had called couldn't find the fault. To be
fair, I think that's because he was as thick as ****.)

Cheers

The pump sounds like it's running, and the temperature both sides feels
about the same. The boiler only runs for a few minutes so it doesn't get
very hot.

Last time I saw a similar failure mode, it was a knackered gas valve.
The test would be to stick a volt meter across the mains input on the
gas valve. If its still got 240V present when it shuts down, then the
valve is knackered.

I lit the pilot and fired up the burner. The voltage on the gas valve
was 240V (white and blue wire if there is a standard).
In failure mode, the burner and pilot go out and the voltage on the
valve remains at 240V.

Would that not to be expected though? The CH controller is still asking
for heat, but for whatever reason the boiler has shut off as it thinks
there is no flame.

If there is mains on the valve, then that means the controls are still
calling for heat. Any additional internal stats in the boiler are
normally placed in series with the call for heat to the valve. So if
there is mains on the valve, it suggests all the other interlocks are
closed.

Even after a failure when the pilot and burner are out, when the CH
controller asks for heat the valve gets 240V, and when it's not asking
for heat the valve gets 0V.

Yup that's what you would expect.

The only bit I am not sure off (since I have never tried it) is what
happens if you have mains on the valve, but then the current from the
thermocouple is withdrawn. That would close the pilot part of the valve,
but I don't know what it would do to the main burner. I am guessing it
would have no effect.

That can't be right can it? Surely if the pilot goes out then all gas must be stopped regardless of whether there is 240V or 0V on the valve.



Robert

On 12/01/2017 14:46, RobertL wrote:
On Monday, January 9, 2017 at 9:54:42 PM UTC, John Rumm wrote:


The only bit I am not sure off (since I have never tried it) is what
happens if you have mains on the valve, but then the current from the
thermocouple is withdrawn. That would close the pilot part of the valve,
but I don't know what it would do to the main burner. I am guessing it
would have no effect.

That can't be right can it? Surely if the pilot goes out then all gas must be stopped regardless of whether there is 240V or 0V on the valve.


Indeed. AIUI, when the thermocouple is hot it holds the pilot valve open
and 'enables' the main valve in some way. It clearly wouldn't be safe
for the main burner to be discharging gas just because the valve is
receiving a 240v demand unless the pilot is also on.

See https://www.youtube.com/watch?v=DLxhKrSEDwE for sort of explanation
- American, but I guess their valves were similar to ours.
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Roger
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On 12/01/2017 00:46, Dave Plowman (News) wrote:
In article ,
Grumps wrote:
On 10/01/2017 23:09, alan_m wrote:
On 09/01/2017 20:32, Grumps wrote:

Its last service was in 2011.
The main burner flames look good to me.


What colour is the main burner flame? Mainly blue? Mainly yellow/orange?

Mainly blue. Can't see the top of the flame though.

When I had this problem, the flame on mine was a normal colour. Only very
small.

Size matters
Mine was clearly too small and being sucked away from the thermocouple
when the main burner started. Then the thermocouple cooled down after a
while, and then the whole thing shut off.
My flame is much bigger now after the gas man blew through it.
It's still working two days later - touch wood.

On 12/01/2017 16:21, Roger Mills wrote:
On 12/01/2017 14:46, RobertL wrote:
On Monday, January 9, 2017 at 9:54:42 PM UTC, John Rumm wrote:


The only bit I am not sure off (since I have never tried it) is what
happens if you have mains on the valve, but then the current from the
thermocouple is withdrawn. That would close the pilot part of the valve,
but I don't know what it would do to the main burner. I am guessing it
would have no effect.

That can't be right can it? Surely if the pilot goes out then all gas
must be stopped regardless of whether there is 240V or 0V on the valve.


Indeed. AIUI, when the thermocouple is hot it holds the pilot valve open
and 'enables' the main valve in some way. It clearly wouldn't be safe
for the main burner to be discharging gas just because the valve is
receiving a 240v demand unless the pilot is also on.

Yup I would not expect it to pass gas on the main valve if the pilot is
not lit - however the only bit I was not certain of what happens if you
extinguish the pilot when the main valve is already lit...

Much would presumably depend on if the main burner will also keep the
thermocouple hot enough to hold the valve open.


See https://www.youtube.com/watch?v=DLxhKrSEDwE for sort of explanation
- American, but I guess their valves were similar to ours.




--
Cheers,

John.

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On 11/01/2017 22:54, John Rumm wrote:
Which is why many modern designs run the case at negative pressure - so
if there is a leak it draws air in, rather than allows combustion
products out.

My old one was positive pressure - but fresh air. The burner was
completely enclosed, and the only way out for combustion products was
the flue - or against a pressure gradient. I never did work out why that
was dangerous - but I was told it was.

Andy

On 12/01/2017 12:04, mechanic wrote:
On Wed, 11 Jan 2017 22:54:38 +0000, John Rumm wrote:

Which is why many modern designs run the case at negative pressure
- so if there is a leak it draws air in, rather than allows
combustion products out.

Can't see any mention of this on the Vaillant or Bosch sites?

On my Vaillant, the fan's induction side is connected to a duct that
stops open ended inside the case. The case is open to the the outer part
of the concentric flue - but the duct is not attached directly to the
inlet. So the fan is actually drawing its combustion air from inside the
case, and that in turn will pull air in through the balanced flue. I
believe this type of design is fairly common these days.


--
Cheers,

John.

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On 12/01/2017 23:13, Vir Campestris wrote:
On 11/01/2017 22:54, John Rumm wrote:
Which is why many modern designs run the case at negative pressure - so
if there is a leak it draws air in, rather than allows combustion
products out.

My old one was positive pressure - but fresh air. The burner was
completely enclosed, and the only way out for combustion products was
the flue - or against a pressure gradient. I never did work out why that
was dangerous - but I was told it was.

One advantage of the fan on the exhaust side is the boiler can be run
safely with the cover off.

On Thu, 12 Jan 2017 23:23:12 +0000, John Rumm wrote:

On 12/01/2017 12:04, mechanic wrote:
On Wed, 11 Jan 2017 22:54:38 +0000, John Rumm wrote:

Which is why many modern designs run the case at negative
pressure - so if there is a leak it draws air in, rather than
allows combustion products out.

Can't see any mention of this on the Vaillant or Bosch sites?

On my Vaillant, the fan's induction side is connected to a duct
that stops open ended inside the case. The case is open to the
the outer part of the concentric flue - but the duct is not
attached directly to the inlet. So the fan is actually drawing
its combustion air from inside the case, and that in turn will
pull air in through the balanced flue. I believe this type of
design is fairly common these days.

The balanced flue connects to the outside world? How does that
ensure under-pressure?

On 13/01/2017 12:45, mechanic wrote:
On Thu, 12 Jan 2017 23:23:12 +0000, John Rumm wrote:

On 12/01/2017 12:04, mechanic wrote:
On Wed, 11 Jan 2017 22:54:38 +0000, John Rumm wrote:

Which is why many modern designs run the case at negative
pressure - so if there is a leak it draws air in, rather than
allows combustion products out.

Can't see any mention of this on the Vaillant or Bosch sites?

On my Vaillant, the fan's induction side is connected to a duct
that stops open ended inside the case. The case is open to the
the outer part of the concentric flue - but the duct is not
attached directly to the inlet. So the fan is actually drawing
its combustion air from inside the case, and that in turn will
pull air in through the balanced flue. I believe this type of
design is fairly common these days.

The balanced flue connects to the outside world? How does that
ensure under-pressure?

The fan sucks air out of the case. The case then draws its from the
flue. The fact that air is flowing via the flue into the case means the
case must be at lower than atmospheric pressure.

Combustion air is being pulled into the pre-mix burner (which is
adjacent to the fan) rather than pushed from a fan at the entry point of
the flue like on older designs.


--
Cheers,

John.

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\================================================= ================/

On 13/01/2017 15:22, John Rumm wrote:
On 13/01/2017 12:45, mechanic wrote:

The balanced flue connects to the outside world? How does that
ensure under-pressure?

The fan sucks air out of the case. The case then draws its from the
flue. The fact that air is flowing via the flue into the case means the
case must be at lower than atmospheric pressure.

Combustion air is being pulled into the pre-mix burner (which is
adjacent to the fan) rather than pushed from a fan at the entry point of
the flue like on older designs.


What about older non-fan-assisted room-sealed boilers with balanced
flues? The airflow is presumably just down to convection. Do they have
negative case pressure?

There must surely be a pressure gradient within the case - with the
bottom being below atmospheric pressure in order to draw fresh air in,
and with the top being above atmospheric pressure in order to expel the
products of combustion?
--
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Roger
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On 13/01/2017 16:23, Roger Mills wrote:
On 13/01/2017 15:22, John Rumm wrote:
On 13/01/2017 12:45, mechanic wrote:

The balanced flue connects to the outside world? How does that
ensure under-pressure?

The fan sucks air out of the case. The case then draws its from the
flue. The fact that air is flowing via the flue into the case means the
case must be at lower than atmospheric pressure.

Combustion air is being pulled into the pre-mix burner (which is
adjacent to the fan) rather than pushed from a fan at the entry point of
the flue like on older designs.


What about older non-fan-assisted room-sealed boilers with balanced
flues? The airflow is presumably just down to convection. Do they have
negative case pressure?

None that I am aware of... And the older style fan assisted flues where
the fan is on the back of the flue and blows air into a duct thence the
burner, don't either AAUI.

There must surely be a pressure gradient within the case - with the
bottom being below atmospheric pressure in order to draw fresh air in,
and with the top being above atmospheric pressure in order to expel the
products of combustion?

What with a non fan convection flue?

Yup - just relying on normal convection caused by the temperature
difference between inlet air temp and flue temp. There is often an
additional inner sealed chamber for the combustion side of the boiler on
those though. My old mexico was like that - so the outer case was not
air tight like on many modern boilers.

--
Cheers,

John.

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