Further problems with my ancient Potterton Profile.

I turned the central heating back on yesterday which may be entirely
irrelevant to the problem as the boiler has been supplying hot water all
summer.

Anyway some time later there was the noise of the boiler actually
boiling and the overheat stat fired. The overheat stat has occasionally
fired in the past (no more than once or twice a year) which I had
previously put down to a barely adequate bypass circuit but I had never
actually heard boiling noises before. I left it for a bit and then reset
the overheat stat with no adverse consequences. However when I was in
the bath last night it did it again which was more than a little odd as
by then the central heating circuit had been switched off and the hot
water was timed off.

Post bath I discovered that as expected the overheat stat had fired
again but on resetting it the boiler fired up even though the programmer
showed that neither the hot water nor the central heating was active.
So I turned the power supply off and went to bed.

This morning I turned the power on again and the boiler immediately
fired up circulating water only round the bypass circuit. Turning on the
central heating and hot water at the programmer resulted in the
appropriate motorised valves opening but turning them off again had no
effect on the boiler at that time. However as I needed both heat and hot
water this morning I switched both circuits on and left the system
running. It has now reverted to working normally so there is nothing I
can now check.

I am currently baffled as to the cause and the fault finding chart in
the installation instructions doesn't cover this eventuality so any
ideas anyone?

--
Roger Chapman

"Roger" wrote in message
k...
Further problems with my ancient Potterton Profile.

I turned the central heating back on yesterday which may be entirely
irrelevant to the problem as the boiler has been supplying hot water all
summer.

Anyway some time later there was the noise of the boiler actually
boiling and the overheat stat fired. The overheat stat has occasionally
fired in the past (no more than once or twice a year) which I had
previously put down to a barely adequate bypass circuit but I had never
actually heard boiling noises before. I left it for a bit and then reset
the overheat stat with no adverse consequences. However when I was in
the bath last night it did it again which was more than a little odd as
by then the central heating circuit had been switched off and the hot
water was timed off.

Post bath I discovered that as expected the overheat stat had fired
again but on resetting it the boiler fired up even though the programmer
showed that neither the hot water nor the central heating was active.
So I turned the power supply off and went to bed.

This morning I turned the power on again and the boiler immediately
fired up circulating water only round the bypass circuit. Turning on the
central heating and hot water at the programmer resulted in the
appropriate motorised valves opening but turning them off again had no
effect on the boiler at that time. However as I needed both heat and hot
water this morning I switched both circuits on and left the system
running. It has now reverted to working normally so there is nothing I
can now check.

I am currently baffled as to the cause and the fault finding chart in
the installation instructions doesn't cover this eventuality so any
ideas anyone?

It could be the micro switch in the motorised valve has failed / becoming
unreliable.

Normally, when the programmer has been set to turn on the CH, it sends power
to the stat, if the stat is calling for heat, it then sends power to the
motorised valve, the valve, when open, then sends power to the boiler and
pump, that then turns on the pump and boiler. If the micro switch in the
valve has failed on, then even with the programmer and stat off, the boiler
can still fire.

Exercising the valve can make it work again, but it may have become
unreliable, so may need it's head, or the complete valve replaced, if the
valve side of it is getting stuck.

How old is the valve?

Toby...

On Fri, 5 Sep 2008 10:44:12 +0100, Toby wrote:

Normally, when the programmer has been set to turn on the CH, it sends
power to the stat, if the stat is calling for heat, it then sends power
to the motorised valve, the valve, when open, then sends power to the
boiler and pump, that then turns on the pump and boiler. If the micro
switch in the valve has failed on, then even with the programmer and
stat off, the boiler can still fire.

Only if the valve microswitch is fed live mains from somewhere that isn't
switched. If it's fed via the programmer and stat then it can only power
the boiler when the programmer is "on" and stat is calling for heat.

Though looking at how I have configured my system the valve switches are
fed with live mains rather than through the programmer and stat. I might
change some jumper positions in the wiring box to stop that incorrect
failure mode. All heavy power switching for the boiler and pumps is done
via relays so the programmer and stat contacts only have to carry the tiny
relay operating load not the 150W boiler and 50W or so pump load. Even so
programmers and stats tend to be 3A inductive rated so switching directly
shouldn't be a problem.

--
Cheers
Dave.

The message
from "Toby" contains these words:

How old is the valve?

I can't remember.

There are 3 valves on the system - upstairs and downstairs heating and
hot water. Over the years I have had to replace one valve complete and
more than one motor but I can't remember which or when and can only
trace one transaction, new motor in 2001. That motor could easily be the
last purchase. The upstairs valve can't be a problem atm as that hasn't
been operated at all over the summer but which of the other two could be
at fault is moot.

Given that for this particular problem the power must be getting through
regardless of the valve motors being on or off is there any other
failure that could have the same results? Otherwise I am tempted to
change both valve heads just in case always assuming I can find heads to
fit. I am not sure who the manufacturers of the current valves are and
may not be able to find out.

--
Roger Chapman

"Roger" wrote in message
k...
The message
from "Toby" contains these words:

How old is the valve?

I can't remember.

There are 3 valves on the system - upstairs and downstairs heating and
hot water. Over the years I have had to replace one valve complete and
more than one motor but I can't remember which or when and can only
trace one transaction, new motor in 2001. That motor could easily be the
last purchase. The upstairs valve can't be a problem atm as that hasn't
been operated at all over the summer but which of the other two could be
at fault is moot.

Given that for this particular problem the power must be getting through
regardless of the valve motors being on or off is there any other
failure that could have the same results? Otherwise I am tempted to
change both valve heads just in case always assuming I can find heads to
fit. I am not sure who the manufacturers of the current valves are and
may not be able to find out.

I replaced the micro switch in one of my valves recently, easy job if you
have a soldering iron.
Maplin stock the switches for a quid or so.

In an earlier contribution to this discussion,
Roger wrote:

The message
from "Toby" contains these words:

How old is the valve?

I can't remember.

There are 3 valves on the system - upstairs and downstairs heating and
hot water. Over the years I have had to replace one valve complete and
more than one motor but I can't remember which or when and can only
trace one transaction, new motor in 2001. That motor could easily be
the last purchase. The upstairs valve can't be a problem atm as that
hasn't been operated at all over the summer but which of the other
two could be at fault is moot.

Given that for this particular problem the power must be getting
through regardless of the valve motors being on or off is there any
other failure that could have the same results? Otherwise I am
tempted to change both valve heads just in case always assuming I can
find heads to fit. I am not sure who the manufacturers of the current
valves are and may not be able to find out.

You clearly have an S-Plan-Plus system with a separate valve for each zone.
Each valve motor will be fed from the programmer and appropriate stat.
Inside each actuator is a micro-switch which closes when the valve is fully
open. These micro-switches have a permanently live feed, and switch on the
boiler and pump whenever one or more is/are closed.

*Now* if any one of those micro-switches fails in the closed position, the
boiler and pump will run regardless of the programmer/stat state. If the
boiler runs with all valves closed (which it *can* do if a micro-switch
fails closed) the water has nowhere to go, and the over-heat stat will trip.
This appears to fit your symptoms exactly.

If the system is now behaving normally - and switching off when all demands
are satisfied - it indicates an inermittent (rather than permanent) failure
of the micro-switch. However beware that it might *appear* to be working
normally if there is a demand from the zone with the failed switch. The acid
test comes when *all* demands are satisfied.
--
Cheers,
Roger
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The message et
from "Dave Liquorice" contains these words:

On Fri, 5 Sep 2008 10:44:12 +0100, Toby wrote:

Normally, when the programmer has been set to turn on the CH, it sends
power to the stat, if the stat is calling for heat, it then sends power
to the motorised valve, the valve, when open, then sends power to the
boiler and pump, that then turns on the pump and boiler. If the micro
switch in the valve has failed on, then even with the programmer and
stat off, the boiler can still fire.

Only if the valve microswitch is fed live mains from somewhere that isn't
switched. If it's fed via the programmer and stat then it can only power
the boiler when the programmer is "on" and stat is calling for heat.

Though looking at how I have configured my system the valve switches are
fed with live mains rather than through the programmer and stat. I might
change some jumper positions in the wiring box to stop that incorrect
failure mode. All heavy power switching for the boiler and pumps is done
via relays so the programmer and stat contacts only have to carry the tiny
relay operating load not the 150W boiler and 50W or so pump load. Even so
programmers and stats tend to be 3A inductive rated so switching directly
shouldn't be a problem.

My microswitches are wired to permanently live.

The downstairs CH valve is a Danfoss. Warranty expired Jan 07.

The DHW valve is a Tower. Might be relatively modern as it has no earth.
(OTOH they might have been making them like that for donkeys years).

Currently working normally. I think I might leave the DHW off for a few
days and then vv with the CH to see if I can isolate the fault but sods
law says I will not get a reoccurrence until both are back on.

--
Roger Chapman

The message
from Roger contains these words:

My microswitches are wired to permanently live.

The downstairs CH valve is a Danfoss. Warranty expired Jan 07.

The DHW valve is a Tower. Might be relatively modern as it has no earth.
(OTOH they might have been making them like that for donkeys years).

Currently working normally. I think I might leave the DHW off for a few
days and then vv with the CH to see if I can isolate the fault but sods
law says I will not get a reoccurrence until both are back on.

As I thought, sods law in full operation.

However when the fault reoccurred I managed to isolate it to the Danfoss
by the simple expedient of removing the programmer and unwiring one side
of the microswitch on each valve. Of course the wiring centre the
Danfoss was wired into was underfloor so it took a bit of effort
shifting furniture and lifting part of the floor.

--
Roger Chapman

"Dave Liquorice" wrote in message
ll.net...
On Fri, 5 Sep 2008 10:44:12 +0100, Toby wrote:

Normally, when the programmer has been set to turn on the CH, it sends
power to the stat, if the stat is calling for heat, it then sends power
to the motorised valve, the valve, when open, then sends power to the
boiler and pump, that then turns on the pump and boiler. If the micro
switch in the valve has failed on, then even with the programmer and
stat off, the boiler can still fire.

Only if the valve microswitch is fed live mains from somewhere that isn't
switched. If it's fed via the programmer and stat then it can only power
the boiler when the programmer is "on" and stat is calling for heat.

Though looking at how I have configured my system the valve switches are
fed with live mains rather than through the programmer and stat.

Which is the way it should be to prevent any feedbacks and not to put heavy
loads on the programmer and stat switches.