Central heating won't turn off

[Simon T]

OK, I know other people have had this problem and have done a cursory Google
search, but have not been able to shed much light on what might be the
problem in my particular case.

Basically, the central heating round at my parents house refuses to switch
off, even when the thermostats aren't calling for heat and the timer is off.
The pump continues to run and the boiler continues to heat the water and the
only way to get it to switch off is to turn everything off at the mains.

I suspected it might have been a stuck 2-port valve, but having checked both
of these found that neither one (CH or DHW) were stuck and appeared to be
operating fine.

Their set up is a standard Gravity Fed System with the feed and expansion
tank in the loft.
Glow Worm hideaway boiler (in a small room next to the kitchen)
Danfoss Electronic Timer (in the kitchen)
Danfoss Room Thermostat (in the Hall)
2x Danfoss 2-port valves (for CH & DHW - in Airing cupboard next to hot
water cylinder)
Danfoss cylinder stat (in airing cupboard)
CH pump (unsure of make - in the airing cupboard)

Again, the 2-port valves were most definitely not jammed open, which was my
first guess. In fact when I went round there to check them, I found my
mother had switched the gas off on the boiler (it didn't occur to her to
switch off the power supply), the timer was off, both 2-port valves were
closed, but the pump was still running?

Any suggestions what to try next?

Thanks in advance.


--
Best Wishes
Simon (Dark Angel)
http://www.realmofhorror.co.uk
http://www.facebook.com/pages/Realm-of-Horror/143030832454357

.

[ARWadsworth]

Have you got a multimeter and do you know how to use one?


--
Adam

* Sometimes I like to lay in my neighbours garden and pretend to be a
carrot *

[Pete Shew]

Is the thermostat wired or wireless?

Pete

[Ben Blaukopf]

The valves might be closing mechanically, but not electrically - the
resistance across brown/orange should be infinite (i.e. open circuit)
when the valve is closed. That still shouldn't cause the pump to run
though, without some other problem!

Take a look here:

http://wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning

And get a multimeter out and start seeing where reality diverges from
what you expect.




However, even if the valve is faulty, if the timer is off then the
pump should still be off, so you either have a wiring fault or a timer
which is lying to you.

I would start by

[Simon T]

"Pete Shew" <psl...@gmail.com> wrote in message ...

> Is the thermostat wired or wireless?

Wired

[Simon T]

"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message...

> Have you got a multimeter and do you know how to use one?

Yes to both!

[Roger Chapman]

On 21/11/2011 16:11, Simon T wrote:

> I suspected it might have been a stuck 2-port valve, but having checked
> both of these found that neither one (CH or DHW) were stuck and appeared
> to be operating fine.

The micro-switch on a 2 port valve could be stuck closed even though the
valve itself had closed which action should have opened the micro-switch
contacts.

--
Roger Chapman

[Roger Mills]

On 21/11/2011 16:11, Simon T wrote:

Each of the zone valves has an auxiliary switch which closes when the
valve is open, and is independent of the motor circuit. These switches
on the two valves are wired in parallel - with a permanent live feed on
the grey wires and a switched live (which switches on the boiler and
pump) on the orange wires.

It's almost certain that one of these switches is stuck in the closed
position - even when its valve is closed. If you disconnect the valves'
grey and orange wires from the junction box, and check for continuity, I
think you'll find the problem - one or other switch is stuck shut.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

[geoff]

In message <_uCdnRJmqNfS5VfT...@bt.com>, Simon T
<darka...@lineone.net> writes

What do you mean by "thermostats"?

What resistance is the temperature sensor showing at the pcb connector?



--
geoff

[The Natural Philosopher]

Ben Blaukopf wrote:
>
>
> However, even if the valve is faulty, if the timer is off then the
> pump should still be off,

No.

thermostats and timers drive the valve, the valve has the high power
contacts that drive the boiler and pump.

Its perfectly possible for the contacts to weld shut so the switch is
closed, even when the valve has shut.

If the system is wired 'correctly; that is in fact the simplest explanation.

physical chafing and shorting of wires being another option.

[Simon T]

"geoff" <tr...@uk-diy.org> wrote in message...

> What do you mean by "thermostats"?

Well there's a thermostat on the wall in the hall which measures the room
temperature, and there's a thermostat attached to the hot water cylinder
which measures the temperature of the hot water that comes out of the tap.

> What resistance is the temperature sensor showing at the pcb connector?

I'll have to check that and get back to you, will next be going round my
parents on Wednesday.

[cynic]

On Nov 21, 4:11 pm, "Simon T" <darkang...@lineone.net> wrote:

> OK, I know other people have had this problem and have done a cursory Google
> search, but have not been able to shed much light on what might be the
> problem in my particular case.
>
> Basically, the central heating round at my parents house refuses to switch
> off, even when the thermostats aren't calling for heat and the timer is off.
> The pump continues to run and the boiler continues to heat the water and the
> only way to get it to switch off is to turn everything off at the mains.
>
> I suspected it might have been a stuck 2-port valve, but having checked both
> of these found that neither one (CH or DHW) were stuck and appeared to be
> operating fine.
>
> Their set up is a standard Gravity Fed System with the feed and expansion
> tank in the loft.

Gravity hot water, pumped heating sounds like a "C plan"
For the hot water to continue heating the hot water valve must be
remaining open. Are you sure the valve is closing when it should? Are
you really sure the hot water primary is gravity circulation?

If the system is actually an "S plan" is there a frost stat somewhere
calling for heat possibly by failure or possibly by inadvertent
alteration.

If you do not have a wiring diagram one should be available on line if
you google.

[Simon T]

"cynic" <icel...@talktalk.net> wrote in message...

> Gravity hot water, pumped heating sounds like a "C plan"

No I meant its gravity fed system (ie uses a feed and expansion tank), as
opposed to be a closed system which is connected directly to the mains. Both
the DHW and CH are pumped.

>For the hot water to continue heating the hot water valve must be
>remaining open.

Both valves were in the closed position when I examined the system, I can
only imagine they were passing slightly if, as my mother said, the rads were
still red hot.

> If the system is actually an "S plan" is there a frost stat somewhere
> calling for heat possibly by failure or possibly by inadvertent
> alteration.

Its an S plan looking at the diagrams posted elsewhere in the thread. Not
aware of a frost stat anywhere on the system.

> If you do not have a wiring diagram one should be available on line if
> you google.

Will do!

[Lieutenant Scott]

On Tue, 22 Nov 2011 09:01:47 -0000, The Natural Philosopher <t...@invalid.invalid> wrote:

> Ben Blaukopf wrote:
>>
>>
>> However, even if the valve is faulty, if the timer is off then the
>> pump should still be off,
>
> No.
>
> thermostats and timers drive the valve, the valve has the high power
> contacts that drive the boiler and pump.

High power contacts? Surely the current required for a pump and the gas solenoid etc in a boiler are not "high power", and could be driven directly from the stat?

> Its perfectly possible for the contacts to weld shut so the switch is
> closed, even when the valve has shut.
>
> If the system is wired 'correctly; that is in fact the simplest explanation.
>
> physical chafing and shorting of wires being another option.

--
http://petersparrots.com
http://petersphotos.com

god said:

"The Divergence of the B Field = 0
The Curl of the E Field + the partial time derivative of the B field = 0
The Divergence of the D field = the charge density
The Curl of the H field - the partial time derivative of the D field = the current density"

and there was light, and he saw that it was good and of constant speed.

[The Natural Philosopher]

Lieutenant Scott wrote:
> On Tue, 22 Nov 2011 09:01:47 -0000, The Natural Philosopher
> <t...@invalid.invalid> wrote:
>
>> Ben Blaukopf wrote:
>>>
>>>
>>> However, even if the valve is faulty, if the timer is off then the
>>> pump should still be off,
>>
>> No.
>>
>> thermostats and timers drive the valve, the valve has the high power
>> contacts that drive the boiler and pump.
>
> High power contacts? Surely the current required for a pump and the gas
> solenoid etc in a boiler are not "high power", and could be driven
> directly from the stat?

start up power for the pumps is quite high.

Everyone does it this way...I guess there is a reason.

The valves have what look like 5A capable microswitches.

Thermostats are much more delicate..well SOME are. Timers also.

I think the rationale is that is not a good idea to have - say - a
motorized valve and a pump in parallel..if the valve goes the pump sits
there pumping into an blocked circuit. Ergo the normal thing is that the
valve is open BEFORE the pump starts..you hear the whirr...the boiler
light goes on..the pump starts,...and then the boiler fires.

[ARWadsworth]

That is the most likely answer.

I went to a job this evening and I just disconnected the orange cables in
turn to identify the faulty 2 port valve.

[The Natural Philosopher]

if you are lucky, you can get just the switch.

Otherwise its a new head job..takes 5 minutes to swap out - no plumbing
required :-)

[ARWadsworth]

I am not going to mess about swapping the switch at work. The customer was
given a price for a new head (Drayton so it's an easy swap). It's a balance
between labour and parts cost and I have to put the customer first.

[Lieutenant Scott]

On Tue, 22 Nov 2011 22:04:12 -0000, The Natural Philosopher <t...@invalid.invalid> wrote:

> Lieutenant Scott wrote:
>> On Tue, 22 Nov 2011 09:01:47 -0000, The Natural Philosopher
>> <t...@invalid.invalid> wrote:
>>
>>> Ben Blaukopf wrote:
>>>>
>>>>
>>>> However, even if the valve is faulty, if the timer is off then the
>>>> pump should still be off,
>>>
>>> No.
>>>
>>> thermostats and timers drive the valve, the valve has the high power
>>> contacts that drive the boiler and pump.
>>
>> High power contacts? Surely the current required for a pump and the gas
>> solenoid etc in a boiler are not "high power", and could be driven
>> directly from the stat?
>
> start up power for the pumps is quite high.
>
> Everyone does it this way...I guess there is a reason.
>
> The valves have what look like 5A capable microswitches.
>
> Thermostats are much more delicate..well SOME are. Timers also.
>
> I think the rationale is that is not a good idea to have - say - a
> motorized valve and a pump in parallel..if the valve goes the pump sits
> there pumping into an blocked circuit.

Yes that makes sense. Just had a look at mine as I'm about to add another radiator - see below. It is wired as above.

I can see another reason for doing it this way. I have two switches in the house - one is for hot water, the other (which is now a thermostat) is for the radiators. If these both switched on the pump directly aswell as the valves, then power would jump across to the wrong valve and they'd both always open, unless the switches were two pole.

The thing is I have never got a bimetal roomstat that will accept the turning on of the motorized valve. I always get an arc in the stat at switchon, which often prevents switchon. I had to get a digital one (with a relay in it). The valve is marked 50 watts. I assume this is the rating of the motor.

> Ergo the normal thing is that the
> valve is open BEFORE the pump starts..you hear the whirr...the boiler
> light goes on..the pump starts,...and then the boiler fires.

I wondered why the boiler didn't start immediately. I guess the motorized valve takes a few seconds to move.

As for the extra radiator - it's in the garage - this will be fun :-)

I'm intending to attach a third motorized valve, which will mean there are three independent pipe circuits, one for the hot water tank, one for the radiators in the house, and one for the garage radiator(s). So any one or any two or all three can be on at once. Easy enough as all the valves and the big ass electrical connection block are in the loft right next to the hatch. The "fun" will be threading the insulated hep pipe through to the garage (there is already quite wide conduit for a wire and the pipe to the tap). I'll have a thermostat in the garage, and one in the house. So the heating will control itself. I just pick two temperatures and leave it forever.

--
http://petersparrots.com
http://petersphotos.com

The success of the "Wonder Bra" for under-endowed women has encouraged the designers to come out with a bra for over-endowed women.
It's called the "Sheep Dog Bra"- it rounds them up and points them in the right direction.

[Simon T]

"Roger Mills" <watt....@gmail.com> wrote in message...

> It's almost certain that one of these switches is stuck in the closed
> position - even when its valve is closed. If you disconnect the valves'
> grey and orange wires from the junction box, and check for continuity, I
> think you'll find the problem - one or other switch is stuck shut.

A quick follow up for those still reading this thread.

Went back round the other day and checked the continuity of the grey &
orange wires on both valve actuators and both were fine.

Got continuity when the valve was open and no continuity when the valve was
shut.

Switched the power back on, system seems to be working again. System shuts
down when the valves are closed.

I'm wondering if my mother buggering about with the programmer might have
had something to do with it not working (though the timer was off when I
checked it out last time when the pump was still running).

[Roger Chapman]

On 26/11/2011 21:41, Simon T wrote:

> A quick follow up for those still reading this thread.
>
> Went back round the other day and checked the continuity of the grey &
> orange wires on both valve actuators and both were fine.
>
> Got continuity when the valve was open and no continuity when the valve
> was shut.
>
> Switched the power back on, system seems to be working again. System
> shuts down when the valves are closed.
>
> I'm wondering if my mother buggering about with the programmer might
> have had something to do with it not working (though the timer was off
> when I checked it out last time when the pump was still running).
>

Well you could get pump overrun for a short time but that would be a few
minutes rather than hours so if it was well after the programmer
switched off then it will have to be an intermittent fault. Intermittent
faults are a pain to trace as they tend to go away just when you think
you have got to the root of the problem.

I have had such a fault for years which causes the overheat stat to fire
as the bypass circuit can't cope if the boiler keeps firing when all the
valves are closed. But it only occurs very occasionally and usually late
at night. I think I have finally cured it having found it in action when
I was forced out of bed in the early hours by bladder pressure but I am
not at my best at 4 in the morning. It was the newest of my 3 two port
valves which I have discounted before because it was so new. Since
changing the head there has not been a recurrence but it is early days yet.

--
Roger Chapman

[Simon T]

"Roger Chapman" <ro...@nospam.zetnet.co.uk> wrote in message...

> Well you could get pump overrun for a short time but that would be a few
> minutes rather than hours so if it was well after the programmer switched
> off then it will have to be an intermittent fault.

Well apparently she seemed to think the heating didn't come on at all the
other morning, so I'm thinking faulty electrical switch on the CH actuator.

But as you say, as the fault is intermittent, it may take a while to pin
down.

Thanks to all those who responded.

[Dave Liquorice]

On Sun, 27 Nov 2011 15:18:41 -0000, Simon T wrote:

> Well apparently she seemed to think the heating didn't come on at all
> the other morning, so I'm thinking faulty electrical switch on the CH
> actuator.

Or the mechanicals have got a bit gummed up and there is quite enough
torque to operate the switch. It could be gunk in the valve shaft to
the wet bit or the rack/pinion that drives the valve open.

--
Cheers
Dave.

[kats...@gmail.com]

My boiler is connected wireless by nest two days ago upstairs heating was variable once ok once could. Today may boiler even thermostat is off. Is working permanent and only downstairs is heating.

[Cynic]

1. You have resurrected a thread from six years ago.
2. Your post makes little sense - is English your first language?

[Brian Gaff]

Its those Russians again.

Brian

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