My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

What could the fault be?
If the stat in the hall failed, which way would it fail? would the
heating go off, or would it go to maximum output?
Could it be a relatively simple matter of replacing that thermostatic
unit?

....a pity because a friend, a retired heating engineer, had visited an
hour before the event!

Thanks

Tony

"tonyjeffs" wrote in message
...
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

What could the fault be?
If the stat in the hall failed, which way would it fail? would the
heating go off, or would it go to maximum output?
Could it be a relatively simple matter of replacing that thermostatic
unit?

...a pity because a friend, a retired heating engineer, had visited an
hour before the event!

Thanks

Tony

Could it be that the thermostat is only connected to the pump. What was the
setting on the boiler thermostat - had someone turned that up high?

I question why you would ever put a room stat at 30 - as such a temp will be
unachievable. Surely 22 should be the max. Likewise 15 could be a bit
chilly.

tell us more about the boiler

tonyjeffs wrote on 21/02/2009 :
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

What could the fault be?
If the stat in the hall failed, which way would it fail? would the
heating go off, or would it go to maximum output?
Could it be a relatively simple matter of replacing that thermostatic
unit?

...a pity because a friend, a retired heating engineer, had visited an
hour before the event!

Two suggestions....

Boiler thermostat turned up to max and max is higher than boiling.
Boiler thermostat is shorted out.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

In article ,
Harry Bloomfield wrote:
Two suggestions....

Boiler thermostat turned up to max and max is higher than boiling.

Sounds a bit strange to me. On older systems it was common to set the
boiler temp to max.

Boiler thermostat is shorted out.

Certainly something faulty.

--
*If you must choose between two evils, pick the one you've never tried before

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

"Dave Plowman (News)" wrote in message
...
In article ,
Harry Bloomfield wrote:
Two suggestions....

Boiler thermostat turned up to max and max is higher than boiling.

Sounds a bit strange to me. On older systems it was common to set the
boiler temp to max.

Boiler thermostat is shorted out.

Certainly something faulty.

--
*If you must choose between two evils, pick the one you've never tried
before

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

If the DHW is gravity operated then it is possible that the primary pipes
are furred up and not letting the heat from the boiler get to the cylinder
fast enough - causing kettling (maybe not boiling)

A helpful development..
My Father in law tells me he had a similar problem with a similar
boiler some years ago. It turned out that the pump, which is outside
the boiler on a readily accessible run of 22mm copper pipe had jammed,
so the water wasn't circulating, so what was in the boiler itself was
bubbling. Could be that.
Easy to access my mom's pump. nudge it with a screwdriver, or replce
it if necessary. It looks about 5 years old to me; not original.

I think I might be getting somewhere - time to get some tools out.

Tony

In article
,
tonyjeffs wrote:
My Father in law tells me he had a similar problem with a similar
boiler some years ago. It turned out that the pump, which is outside
the boiler on a readily accessible run of 22mm copper pipe had jammed,
so the water wasn't circulating, so what was in the boiler itself was
bubbling. Could be that.

Assuming an old basic system, the wall stat simply switches the pump - so
the pump stopping shouldn't cause the boiler any problems.

--
*There are two kinds of pedestrians... the quick and the dead.

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

In message
,
tonyjeffs writes
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

What could the fault be?
If the stat in the hall failed, which way would it fail? would the
heating go off, or would it go to maximum output?
Could it be a relatively simple matter of replacing that thermostatic
unit?

...a pity because a friend, a retired heating engineer, had visited an
hour before the event!

there's your problem ...

p.s. he's a fitter, not as engineer


Thanks

Tony

--
geoff

Hi Dave mainly

I don't yet understand the circuit.
There is what looks like a thermostat linked to the immersion heater,
and this is wired to a pump. This is all in a first floor cupboard
I don't understand how switching this pump on and off would protect
the boiler (which is downstairs). gravity and convection would help,
but I would've thought that for adequate protection agsinst
overheating, there must be forced circulation while the gas is
burning.
....Not doubting you at all... I just need to understand it for myself
before upping tools.

I'm away until Thursday, so will mull it over till then. My mom is ok,
since she has electric hot water from the immersion, and has a decent
gas fire. Central heating - who needs it anyway!

Thanx again

Tony

tonyjeffs wrote:
Hi Dave mainly

I don't yet understand the circuit.
There is what looks like a thermostat linked to the immersion heater,
and this is wired to a pump. This is all in a first floor cupboard
I don't understand how switching this pump on and off would protect
the boiler (which is downstairs). gravity and convection would help,
but I would've thought that for adequate protection agsinst
overheating, there must be forced circulation while the gas is
burning.
...Not doubting you at all... I just need to understand it for myself
before upping tools.

I'm away until Thursday, so will mull it over till then. My mom is ok,
since she has electric hot water from the immersion, and has a decent
gas fire. Central heating - who needs it anyway!

Thanx again

Tony

I think you need to work out what type of circulation system you have.

Thermostas are almost NEVER connected to pumps directly.

The normal way things are, is that timers switch to thermostats, and via
the to motorised VALVES which open and close water circuits, and having
opened them switch on a circulation pump for the whole boiler system.
That runs as long as there is call for heat for anything the boiler
needs to control. Then the boiler will fire up until the RETURN
temperature of the water, as seen by the boilers own thermostat in
conjunction with its heat setting, gets to whatever its set to.

There is no way a boiler should boil as such. The only way it ca is if
the circulation stops, and so there is no return flow at all: then it
will fire until the heat exchanger nearly boils, at which time the
return flow sensing will get got by heat travelling backwards and cut it.

TBH what the user is reporting makes little sense..

"The Natural Philosopher" wrote in message
...
tonyjeffs wrote:
Hi Dave mainly

I don't yet understand the circuit.
There is what looks like a thermostat linked to the immersion heater,
and this is wired to a pump. This is all in a first floor cupboard
I don't understand how switching this pump on and off would protect
the boiler (which is downstairs). gravity and convection would help,
but I would've thought that for adequate protection agsinst
overheating, there must be forced circulation while the gas is
burning.
...Not doubting you at all... I just need to understand it for myself
before upping tools.

I'm away until Thursday, so will mull it over till then. My mom is ok,
since she has electric hot water from the immersion, and has a decent
gas fire. Central heating - who needs it anyway!

Thanx again

Tony

I think you need to work out what type of circulation system you have.

Thermostas are almost NEVER connected to pumps directly.

The normal way things are, is that timers switch to thermostats, and via
the to motorised VALVES which open and close water circuits, and having
opened them switch on a circulation pump for the whole boiler system. That
runs as long as there is call for heat for anything the boiler needs to
control. Then the boiler will fire up until the RETURN temperature of the
water, as seen by the boilers own thermostat in conjunction with its heat
setting, gets to whatever its set to.

But that is only normal for systems installed in the last 25 years. Older
systems used a gravity loop for the HW and a pump for the CH. The thermostat
was connected directly to the pump in these systems.


There is no way a boiler should boil as such. The only way it ca is if the
circulation stops, and so there is no return flow at all: then it will
fire until the heat exchanger nearly boils, at which time the return flow
sensing will get got by heat travelling backwards and cut it.

It will boil if the boiler stat if shorted out or faulty.

TBH what the user is reporting makes little sense..

More info on his system is needed. An immersion heater linked to a pump and
to a thermostat seems very odd and most unlikely.

Adam

"ARWadsworth" wrote in message
om...

"The Natural Philosopher" wrote in message
...
tonyjeffs wrote:
Hi Dave mainly

I don't yet understand the circuit.
There is what looks like a thermostat linked to the immersion heater,
and this is wired to a pump. This is all in a first floor cupboard
I don't understand how switching this pump on and off would protect
the boiler (which is downstairs). gravity and convection would help,
but I would've thought that for adequate protection agsinst
overheating, there must be forced circulation while the gas is
burning.
...Not doubting you at all... I just need to understand it for myself
before upping tools.

I'm away until Thursday, so will mull it over till then. My mom is ok,
since she has electric hot water from the immersion, and has a decent
gas fire. Central heating - who needs it anyway!

Thanx again

Tony

I think you need to work out what type of circulation system you have.

Thermostas are almost NEVER connected to pumps directly.

The normal way things are, is that timers switch to thermostats, and via
the to motorised VALVES which open and close water circuits, and having
opened them switch on a circulation pump for the whole boiler system.
That runs as long as there is call for heat for anything the boiler needs
to control. Then the boiler will fire up until the RETURN temperature of
the water, as seen by the boilers own thermostat in conjunction with its
heat setting, gets to whatever its set to.

But that is only normal for systems installed in the last 25 years. Older
systems used a gravity loop for the HW and a pump for the CH. The
thermostat was connected directly to the pump in these systems.


There is no way a boiler should boil as such. The only way it ca is if
the circulation stops, and so there is no return flow at all: then it
will fire until the heat exchanger nearly boils, at which time the return
flow sensing will get got by heat travelling backwards and cut it.

It will boil if the boiler stat if shorted out or faulty.

TBH what the user is reporting makes little sense..

More info on his system is needed. An immersion heater linked to a pump
and to a thermostat seems very odd and most unlikely.

Adam


Is it a Back Boiler? What is the Boiler thermostat set to?

In article ,
The Natural Philosopher wrote:
Thermostas are almost NEVER connected to pumps directly.

That's ********. On the most basic system - with 'gravity' hot water -
that's exactly how it works.
With Y plan it still does - but you switch between two stats - one for the
heating and one for the hot water.

--
*Don't sweat the petty things and don't pet the sweaty things.

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

In article
,
tonyjeffs wrote:
Hi Dave mainly

I don't yet understand the circuit.
There is what looks like a thermostat linked to the immersion heater,
and this is wired to a pump.

The immersion heater is entirely separate from the heating system and can
be ignored. It has its own internal thermostat. Or rather that's the case
in 99.9% of setups.

If there is an electrical thermostat fitted to the cylinder you'll likely
have an S or Y plan system. The FAQ gives details.


This is all in a first floor cupboard
I don't understand how switching this pump on and off would protect
the boiler (which is downstairs). gravity and convection would help,
but I would've thought that for adequate protection agsinst
overheating, there must be forced circulation while the gas is
burning.

No. On older systems the boiler can be totally self contained. Ie it
cycles away to itself maintaining a set water temperature. But you appear
to have a more sophisticated system which should only fire the boiler when
there is a call for heat from either the heating or hot water. However,
the boiler thermostat is still needed to prevent the water in that
overheating. In other words the boiler can't dump all its output into the
heating or hot water circuit at all times so needs a way of controlling
that. A modern boiler achieves this by turning down the flame - older ones
by switching it on and off.

...Not doubting you at all... I just need to understand it for myself
before upping tools.

I'm away until Thursday, so will mull it over till then. My mom is ok,
since she has electric hot water from the immersion, and has a decent
gas fire. Central heating - who needs it anyway!

Anyone not sat in front of the gas fire? ;-)

--
*I wish the buck stopped here. I could use a few.

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

tonyjeffs wrote:
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

What could the fault be?

Sounds like a gravity HW system with a pumped CH ring (controlled by the
wall stat).

The boiler stat is either stuck of set way too high but that's been masked
by the CH system carrying away heat fast enough to stop the boiler
overheating. By turning the wall stat down, the boiler is now being
controlled (or not as the case may be) by the boiler stat.

Check the boiler stat (which will probably be inside the boiler cabinet).
Does it click when turned? Does the boiler shut down when you turn it down?

If it doesn't click or the boiler doesn't shut down then the boiler stat is
faulty. It could just be set way too high but I would have though that aby
boiler stat ought to shut off a boiler before it boils (literally).

Tim

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "ARWadsworth"
saying something like:

More info on his system is needed. An immersion heater linked to a pump and
to a thermostat seems very odd and most unlikely.

Probably the stat/pump feed is taken from the immersion supply.

On Feb 21, 2:12*am, tonyjeffs wrote:
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. *She turned it all off.


People are discussing the boiler overheating, but it's the hot water
cylinder that is making the boiling noises not the boiler.

I would suspect a faulty immersion heater thermostat.

Robert

RobertL wrote:
On Feb 21, 2:12 am, tonyjeffs wrote:
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water
in the immersion cylender had sounded like it was boiling and about
to explode. She turned it all off.


People are discussing the boiler overheating, but it's the hot water
cylinder that is making the boiling noises not the boiler.

I would suspect a faulty immersion heater thermostat.

The immersion heater wasn't in use at that time. He's only been using it
since the boiler boiled.

Tim

"Tim Downie" wrote in message
...
RobertL wrote:
On Feb 21, 2:12 am, tonyjeffs wrote:
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water
in the immersion cylender had sounded like it was boiling and about
to explode. She turned it all off.


People are discussing the boiler overheating, but it's the hot water
cylinder that is making the boiling noises not the boiler.

I would suspect a faulty immersion heater thermostat.

The immersion heater wasn't in use at that time. He's only been using it
since the boiler boiled.

Tim



From what I remember when we had a coke fired Aga type of thing the boiling
sounds did come from the cylinder if it got a bit too hot - however - it
wasn't a proper indirect cylinder and we got brown water if it got too hot.

On Fri, 20 Feb 2009 18:12:16 -0800 (PST), tonyjeffs wrote:

My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. She turned it all off.

It's an old system so you can pretty much forget how modern systems are
wired up.

she told me that the heating had gone incredibbly hot......

What exactly happened? Is the boiler turned on all day? Were the rads
getting very hot? Was it just the cylinder getting very hot? Without that
info it's not possible to make a sensible diagnosis of the problem.

--
The Wanderer

I have seen the truth - it doesn't make sense

On 23 Feb, 17:18, The Wanderer wrote:
On Fri, 20 Feb 2009 18:12:16 -0800 (PST), tonyjeffs wrote:
My mom's central heating is 25 years old, but has been working well.
Yesterday I turned the hall thermostat down from 30 to 15. I left.
When I revisited later in the day, she told me that the heating had
gone incredibbly hot, started making worrying noises, and the water in
the immersion cylender had sounded like it was boiling and about to
explode. *She turned it all off.

It's an old system so you can pretty much forget how modern systems are
wired up.

she told me that the heating had gone incredibbly hot......

What exactly happened? Is the boiler turned on all day? Were the rads
getting very hot? Was it just the cylinder getting very hot? Without that
info it's not possible to make a sensible diagnosis of the problem.

--
The Wanderer

I have seen the truth - it doesn't make sense

I wasn't there, but here's new information:

1.The boiler stat seems to be working. If I turn the dial (0 to 6
scale), it'll click at some point and the burner shut off.
2. The Immersion heater was not in use at the time
3. The pump in the immersion cupboard is working fine on each of its
three settings
4. My mom told me today that because my sister was coming to visit and
stay, she'd turned the boiler and wall stat up to their maximum
settings. I would think the ch ought to have some safety cut-out for
such eventualities, but I've instructed her in the correct use of the
system. I've had it running all day without a problem. Nice hot rads,
and plenty of hot water at a setting of just '2'. No need to turn it
higher under any circumstances. I think that'll be ok for now. Mum
is happilywarm again, and is going to take out a British Gas
maintenance contract for £12/month. So I don't have to do any work :-)

Thanks again
Tony