(yes I know it's 35 years old and needs replacing - I'm just trying to nurse
it through until spring!)

The boiler is overheating (radiators too hot, HW scalding and boiler
creaking a bit). The room and HW cylinder thermostats are working ok, so I
thought the problem was the boiler thermostat. Replaced it with a new one
last week but problem still persists. If I turn the boiler thermostat down
to zero it clicks off and the boiler shuts down, but putting it to any other
setting from 1 to 6 the boiler just keeps going until the room/cylinder stat
shuts it down. Turning the knob through it's range there's no feel/sound of
it switching as I'm sure the old one used to do. I suppose the new
thermostat could be faulty - any way of testing it?

I have recently flushed the system in anticipation of getting a new boiler,
but then plans delayed so I refilled with new inhibitor. When draining the
system I found both the drain tap on the lowest rad and the one on the
boiler frozen/blocked, so I fitted a new one on the rad but didn't bother
with the boiler one (at the time though at new boiler was imminent). Could
there be an air lock or sludge in the boiler which is somehow affecting the
thermostat but still allowing the boiler to produce (very) hot water?

Grateful for any advice.
David
(remove _notme from email address)

In article <63u%e.8169$0w.6587@newsfe5-gui.ntli.net>,
	"DavidM"  writes:

>(yes I know it's 35 years old and needs replacing - I'm just trying to nurse
>it through until spring!)
>
>The boiler is overheating (radiators too hot, HW scalding and boiler
>creaking a bit). The room and HW cylinder thermostats are working ok, so I
>thought the problem was the boiler thermostat. Replaced it with a new one
>last week but problem still persists. If I turn the boiler thermostat down
>to zero it clicks off and the boiler shuts down, but putting it to any other
>setting from 1 to 6 the boiler just keeps going until the room/cylinder stat
>shuts it down. Turning the knob through it's range there's no feel/sound of
>it switching as I'm sure the old one used to do. I suppose the new
>thermostat could be faulty - any way of testing it?


What sort is it? Does it have a phile on the end of a thin
copper tube? If so, test it by dunking the phile in a mug
of hot water with a separate thermometer. The temperature
range from min to max should probably be something like
60C through to 80C or 85C.

-- 
Andrew Gabriel

If I turn the boiler thermostat down

> to zero it clicks off and the boiler shuts down, but putting it to any
other
> setting from 1 to 6 the boiler just keeps going until the room/cylinder
stat
> shuts it down. Turning the knob through it's range there's no feel/sound
of
> it switching as I'm sure the old one used to do. I suppose the new
> thermostat could be faulty - any way of testing it?


Could be faulty, it's not unheard of. I'd be looking for a dodgy connection
to/from the stat in the first instance.

Having just tried mine ( different system altogether ) I realise that the
boiler stat only clicks when the water temp is up. Otherwise the click is
off the scale to the low end all the time, if that makes sense. You could
try running the boiler for say 20 mins and then see if you can get the stat
to click. However, that will only tell you that the stat is sensing
temperature, not that it would be in a position to shut down the system.

At the other end of the circuit from the stat there must be some sort of
valve or servo that actually turns the system off and it may be that end
that's faulty.

TonyB

In an earlier contribution to this discussion,
DavidM   wrote:


> (yes I know it's 35 years old and needs replacing - I'm just trying
> to nurse it through until spring!)
>
> The boiler is overheating (radiators too hot, HW scalding and boiler
> creaking a bit). The room and HW cylinder thermostats are working ok,
> so I thought the problem was the boiler thermostat. Replaced it with
> a new one last week but problem still persists. If I turn the boiler
> thermostat down to zero it clicks off and the boiler shuts down, but
> putting it to any other setting from 1 to 6 the boiler just keeps
> going until the room/cylinder stat shuts it down. Turning the knob
> through it's range there's no feel/sound of it switching as I'm sure
> the old one used to do. I suppose the new thermostat could be faulty
> - any way of testing it?
>
> I have recently flushed the system in anticipation of getting a new
> boiler, but then plans delayed so I refilled with new inhibitor. When
> draining the system I found both the drain tap on the lowest rad and
> the one on the boiler frozen/blocked, so I fitted a new one on the
> rad but didn't bother with the boiler one (at the time though at new
> boiler was imminent). Could there be an air lock or sludge in the
> boiler which is somehow affecting the thermostat but still allowing
> the boiler to produce (very) hot water?
>
> Grateful for any advice.
> David
> (remove _notme from email address)


Silly question: I suppose the little bulb on the end of the stat's capillary
tube *is* correctly plugged into its hole in the heat exchanger - so that it
senses the boiler temperature? Is it making good contact. [You used to be
able to get some heat conducting paste to put in the hole to make sure that
it contacts ok. Probably still can!]
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"DavidM"  wrote in message
news:63u%e.8169$0w.6587@newsfe5-gui.ntli.net...

> (yes I know it's 35 years old and needs replacing - I'm just trying to
nurse
> it through until spring!)
>
> The boiler is overheating (radiators too hot, HW scalding and boiler
> creaking a bit). The room and HW cylinder thermostats are working ok, so I
> thought the problem was the boiler thermostat. Replaced it with a new one
> last week but problem still persists. If I turn the boiler thermostat down
> to zero it clicks off and the boiler shuts down, but putting it to any
other
> setting from 1 to 6 the boiler just keeps going until the room/cylinder
stat
> shuts it down. Turning the knob through it's range there's no feel/sound
of
> it switching as I'm sure the old one used to do. I suppose the new
> thermostat could be faulty - any way of testing it?
>
> I have recently flushed the system in anticipation of getting a new
boiler,
> but then plans delayed so I refilled with new inhibitor. When draining the
> system I found both the drain tap on the lowest rad and the one on the
> boiler frozen/blocked, so I fitted a new one on the rad but didn't bother
> with the boiler one (at the time though at new boiler was imminent). Could
> there be an air lock or sludge in the boiler which is somehow affecting
the
> thermostat but still allowing the boiler to produce (very) hot water?
>
> Grateful for any advice.
> David
> (remove _notme from email address)
>
>

Thanks for replies so far.
I've done some more checks:
1. Removed thermostat and checked it in a pan of hot water and with a
meter - switches correctly between 60 and 80 C. The old thermostat I took
out also works correctly grrrrrrrr - 33 needlessly spent!
2. Checked the electrical connections - the boiler gas valve is only
connected to the bioler thermostat, no where else, so nothing can be
bypassing the thermostat.
3. Checked that the thermostat bulb is pushed fully into the tube in the
boiler.
4. The gas valve turns off if the boiler supply is swithed off or if the
boiler thermostat is turned to the off position, so I'm pretty sure it's not
just the gas valve sticking (the whole gas valve assembly was renewed last
year anyway).

Any more ideas please?
David
(remove _notme from email address)

In article <toP%e.397$rp1.130@newsfe4-win.ntli.net>,
	"DavidM"  writes:

>Thanks for replies so far.
>I've done some more checks:
>1. Removed thermostat and checked it in a pan of hot water and with a
>meter - switches correctly between 60 and 80 C. The old thermostat I took
>out also works correctly grrrrrrrr - 33 needlessly spent!
>2. Checked the electrical connections - the boiler gas valve is only
>connected to the bioler thermostat, no where else, so nothing can be
>bypassing the thermostat.
>3. Checked that the thermostat bulb is pushed fully into the tube in the
>boiler.
>4. The gas valve turns off if the boiler supply is swithed off or if the
>boiler thermostat is turned to the off position, so I'm pretty sure it's not
>just the gas valve sticking (the whole gas valve assembly was renewed last
>year anyway).
>
>Any more ideas please?


Would be useful to narrow down a thermal problem or an electrical problem.
If you take the phile out of the tube and dunk it into a mug of nearly
boiling water, does that cut off the gas valve?
(Obviously, take care with mugs of water and mains around.)

-- 
Andrew Gabriel

In an earlier contribution to this discussion,
DavidM   wrote:


>>
> Thanks for replies so far.
> I've done some more checks:
> 1. Removed thermostat and checked it in a pan of hot water and with a
> meter - switches correctly between 60 and 80 C. The old thermostat I
> took out also works correctly grrrrrrrr - 33 needlessly spent!
> 2. Checked the electrical connections - the boiler gas valve is only
> connected to the bioler thermostat, no where else, so nothing can be
> bypassing the thermostat.
> 3. Checked that the thermostat bulb is pushed fully into the tube in
> the boiler.
> 4. The gas valve turns off if the boiler supply is swithed off or if
> the boiler thermostat is turned to the off position, so I'm pretty
> sure it's not just the gas valve sticking (the whole gas valve
> assembly was renewed last year anyway).
>
> Any more ideas please?
> David


So the thermostat works when you test it in water. The output from the stat
is the only thing connected to the gas valve - but when the boiler gets hot,
the stat doesn't switch off when it should. Is that correct?

If so, it can *only* be that the stat is not sensing the temperature of the
boiler for some reason. Try cleaning out its pocket with a suitable sized
drill bit (operated by hand!) to make sure there's no gunge in there that's
providing insulation and preventing proper contact. Then use some heat
conducting paste.

It that doesn't work, it sounds like there could be some sludge inside the
heat exchanger which is stopping the hot water from getting to the area of
the thermostat pocket.
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

> Would be useful to narrow down a thermal problem or an electrical problem.
> If you take the phile out of the tube and dunk it into a mug of nearly
> boiling water, does that cut off the gas valve?
> (Obviously, take care with mugs of water and mains around.)



Andrew's idea sounds like a good test, can you do that one?
TonyB

On Sun, 02 Oct 2005 13:01:57 +0100, Set Square wrote:


> In an earlier contribution to this discussion,
> DavidM   wrote:
> 
>>>
>> Thanks for replies so far.
>> I've done some more checks:
>> 1. Removed thermostat and checked it in a pan of hot water and with a
>> meter - switches correctly between 60 and 80 C. The old thermostat I
>> took out also works correctly grrrrrrrr - 33 needlessly spent!
>> 2. Checked the electrical connections - the boiler gas valve is only
>> connected to the bioler thermostat, no where else, so nothing can be
>> bypassing the thermostat.
>> 3. Checked that the thermostat bulb is pushed fully into the tube in
>> the boiler.
>> 4. The gas valve turns off if the boiler supply is swithed off or if
>> the boiler thermostat is turned to the off position, so I'm pretty
>> sure it's not just the gas valve sticking (the whole gas valve
>> assembly was renewed last year anyway).
>>
>> Any more ideas please?
>> David
> 
> So the thermostat works when you test it in water. The output from the stat
> is the only thing connected to the gas valve - but when the boiler gets hot,
> the stat doesn't switch off when it should. Is that correct?
> 
> If so, it can *only* be that the stat is not sensing the temperature of the
> boiler for some reason. Try cleaning out its pocket with a suitable sized
> drill bit (operated by hand!) to make sure there's no gunge in there that's
> providing insulation and preventing proper contact. Then use some heat
> conducting paste.
> 
> It that doesn't work, it sounds like there could be some sludge inside the
> heat exchanger which is stopping the hot water from getting to the area of
> the thermostat pocket.


The only other possibility is that the capiliary tube is kinked so that
when the thermostat is in position it  does not work correctly?



-- 
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