Hello,
I'd really appreciate some help with my central heating boiler.

I have a Vaillant ThermoCompact VC GB 112 EH, with a Danfoss FP715
timer unit.

Most of the time the boiler works fine. Now and then, it will stop
working completely, for a couple of days or so, and then start working
again.

I've called out two plumbers to have a look at the system, but they
haven't been able to shed any light on the issue.

It seems to me that whenever the central heating or hot water is
"advanced" for an hour (ie when it's activated outside of the usual
timings, for example at the weekend if we're in the house during the
day), then the next time the hot water or central heating come on as
scheduled (usually the next morning), then the boiler cuts out after
having heated the water only to luke warm.

The boiler then refuses to light.

Anyone got any ideas? I'm freezing! Although it will probably be
working again in a couple of days.

Thanks in advance.

Chris

In an earlier contribution to this discussion,
Chris wrote:

Hello,
I'd really appreciate some help with my central heating boiler.

I have a Vaillant ThermoCompact VC GB 112 EH, with a Danfoss FP715
timer unit.

Most of the time the boiler works fine. Now and then, it will stop
working completely, for a couple of days or so, and then start working
again.

I've called out two plumbers to have a look at the system, but they
haven't been able to shed any light on the issue.

It seems to me that whenever the central heating or hot water is
"advanced" for an hour (ie when it's activated outside of the usual
timings, for example at the weekend if we're in the house during the
day), then the next time the hot water or central heating come on as
scheduled (usually the next morning), then the boiler cuts out after
having heated the water only to luke warm.

The boiler then refuses to light.

Anyone got any ideas? I'm freezing! Although it will probably be
working again in a couple of days.

Thanks in advance.

Chris

We need to know a bit more about the rest of your system. Is it fully
pumped? If so, does it have 2 zone valves (S-Plan see
http://content.honeywell.com/uk/homes/systems.htm) or one 3-port
mid-position valve (Y-Plan)?

When the boiler fails to light, is it receiving a "go" signal from the rest
of the system - in other words, is its Switched Live connection live? This
is important, because it isolates the problem either to the boiler itself or
to the external controls.

Are you sure that the cylinder and room thermostats are working ok?
--
Cheers,
Set Square
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On Tue, 9 Nov 2004 12:06:12 -0000, "Set Square" wrote:

In an earlier contribution to this discussion,
Chris wrote:

Hello,
I'd really appreciate some help with my central heating boiler.

I have a Vaillant ThermoCompact VC GB 112 EH, with a Danfoss FP715
timer unit.

Most of the time the boiler works fine. Now and then, it will stop
working completely, for a couple of days or so, and then start working
again.

I've called out two plumbers to have a look at the system, but they
haven't been able to shed any light on the issue.

It's probably an electrical or control equipment fault then. Plumbers
deal mainly with pipework; you need a central heating engineer. People
here will be more than willing to help, but as "Set Square" says, we
need more info from you to work on.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me

Is it fully pumped? If so, does it have 2 zone valves (S-Plan see
http://content.honeywell.com/uk/homes/systems.htm) or one 3-port
mid-position valve (Y-Plan)?

I'm fairly sure I have a fully pumped, S-plan system (there are
definitely two valves and hot water and central heating are
independant of each other.

I'm not sure what you mean by "is its Switched Live connection live?"
I attempted to start the boiler by setting the timer for the central
heating/hot water to come on and by "advancing" hot water / central
heating. In both cases, the boiler failed to light.

Are you sure that the cylinder and room thermostats are working ok?

Well, having switched off the boiler at the mains for a while, and
then switched it on again, hot water and central heating have both
come on as per the timer.

I don't know if this will help, but when it wasn't working, the boiler
sounded as though it was "stuck" - the fan was going and it seemed
about to spark up, but didn't actually get that far, even though
central heating and hot water were not due to come on at this time.
Turning off the mains supply for an hour or so appears to have "reset"
the boiler, so when the mains was switched back on, the boiler didn't
make any attempt to start...until the timer instructed it to do so a
few hours later.

Any help is very much appreciated. Thanks for your time so far.

In an earlier contribution to this discussion,
Chris wrote:


I'm not sure what you mean by "is its Switched Live connection live?"

There should be a multi-core cable connected to the boiler. One of the cores
is the "switched live" (as opposed to a permanent live) connection - and is
at mains voltage whenever the external control equipment (timer,
thermostats, zone valves) is collectively calling for heat. You will need a
boiler circuit diagram and a volt meter to be able to answer the question.

If this signal *is* present, but the boiler isn't lighting, there's a
problem with the boiler itself.

If this signal is *not* present when the programmer and stats are all
calling for heat, there's a problem external to the boiler - either a wiring
fault or a failure of a thermostat or zone valve.



I don't know if this will help, but when it wasn't working, the boiler
sounded as though it was "stuck" - the fan was going and it seemed
about to spark up, but didn't actually get that far, even though
central heating and hot water were not due to come on at this time.

This is very odd! If the programmer and stats are OFF, the boiler should not
be trying to light - unless, perhaps, there is a frost stat somewhere which
brings the heating on regardless of the state of the programmer.

Maybe you have more than one fault!

If your system *is* an S-Plan, you will see from the reference I quoted
earlier that the programmer and stats simply drive the zone valves. Each
zone valve has an independent set of contacts which close when the valve is
open. These contacts turn the boiler and pump on. If one of your zone valves
is stuck open (maybe the spring return is a bit sluggish), it *could* turn
the boiler on even when the programmer is off.

If the boiler's fan is running, the boiler must be being told to light. I
don't know your particular boiler, but I assume that it has a fan-assisted
flue. In order to light, a certain sequence of events has to occur.
Typically, the fan runs and generates enough pressure to operate a pressure
switch which switches on the pilot gas valve and the spark mechanism. A bit
of electronics - using flame ionisation or some such similar wizardry - then
turns on the main gas valve, and bingo! The whole thing can fail at any
stage along the way. If you have an unstallation manual for the boiler, it
should have some diagnostic charts to help you to pin-point the problem.

You can sometimes find out what is happening simply by switching things on
and off, but this is often inconclusive - and you need to roll up your
sleeves and get *inside* the system - or find others who know what they are
doing to diagnose it for you.
--
Cheers,
Set Square
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You require a heating engineer
Thanks, yes, I realise this...when I said plumber I meant heating
engineer. My 2nd engineer is a good bloke and knows what he's doing,
but it's difficult for him to diagnose the problem as each time he's
been round the boiler's working again.

There should be a multi-core cable connected to the boiler...
I'll check this out.

This is very odd!
You're telling me! It's very confusing.

If your system *is* an S-Plan, you will see from the reference I quoted
earlier that the programmer and stats simply drive the zone valves. Each
zone valve has an independent set of contacts which close when the valve is
open. These contacts turn the boiler and pump on. If one of your zone valves
is stuck open (maybe the spring return is a bit sluggish), it *could* turn
the boiler on even when the programmer is off.

This sounds like a possibility...so you're saying that the programmer
and stats drive the valves, and these drive the boiler? As everything
else seems to work this could be the problem. Maybe one of the valves
is closing prematurely once I've advanced the heating or hot water?

In order to light, a certain sequence of events has to occur.
Yes - a few things happen...I (with the help of engineer no.1) first
thought that the fan control circuit board was faulty, so this was
replaced then I thought the air pressure switch was faulty, but since
the boiler works consistently (for weeks at a time) until after it's
"advanced", I don't think there's anything wrong with the boiler
itself. The thing is, the boiler comes on as programmed after it's
advanced, but cuts out before it's finished heating the water.

If you have an unstallation manual for the boiler, it
should have some diagnostic charts to help you to pin-point the problem.

I've gone through the diagnostics, as have both my engineers, and it
hasn't really helped.

You can sometimes find out what is happening simply by switching things on
and off

I've tried this too, as have my engineers.

I think the thing to do is to wait till it's not working and call out
my engineer again.

But if anyone has any other ideas please let me know.

Thanks very much for your help and time so far.

In an earlier contribution to this discussion,
Chris wrote:


This sounds like a possibility...so you're saying that the programmer
and stats drive the valves, and these drive the boiler?

Yes. You can see this if you study the S-Plan wiring diagram in
http://content.honeywell.com/uk/homes/systems.htm

The switches inside the zone valves (which make when the valves have been
driven open by the programmer/stat) have a permanent live feed from (1) in
the junction box, and feed this to (10) - and thence to the boiler and
pump - when the switch is closed.
--
Cheers,
Set Square
______
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On Tue, 09 Nov 2004 02:22:26 -0800, Chris wrote:

Hello,
I'd really appreciate some help with my central heating boiler.

I have a Vaillant ThermoCompact VC GB 112 EH, with a Danfoss FP715
timer unit.

Most of the time the boiler works fine. Now and then, it will stop
working completely, for a couple of days or so, and then start working
again.

I've called out two plumbers to have a look at the system, but they
haven't been able to shed any light on the issue.

It seems to me that whenever the central heating or hot water is
"advanced" for an hour (ie when it's activated outside of the usual
timings, for example at the weekend if we're in the house during the
day), then the next time the hot water or central heating come on as
scheduled (usually the next morning), then the boiler cuts out after
having heated the water only to luke warm.

The boiler then refuses to light.

Anyone got any ideas? I'm freezing! Although it will probably be
working again in a couple of days.

Thanks in advance.

I'd split the problem between the boiler and the controls.
I'm fairly sure that on this model boiler joining terminals 3 and 4
together brings on the heating.

So find out how the controls are meant to work and then see if they are
doing it right.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

On Wed, 10 Nov 2004 12:55:29 +0000, Set Square wrote:

In an earlier contribution to this discussion,
Chris wrote:


This sounds like a possibility...so you're saying that the programmer
and stats drive the valves, and these drive the boiler?

Yes. You can see this if you study the S-Plan wiring diagram in
http://content.honeywell.com/uk/homes/systems.htm

The switches inside the zone valves (which make when the valves have been
driven open by the programmer/stat) have a permanent live feed from (1) in
the junction box, and feed this to (10) - and thence to the boiler and
pump - when the switch is closed.

I'm fairly sure that this Vaillant will be like all others - boiler go is
performed by joining a pair of terminals.

For S-plan this means those terminals should connect to the grey and
orange wires of the zone valves.

Given that people have been down the diagnostics check list for the boiler
that would imply that the external controls are giving the right signal to
the boiler. (Invariably the check list is something like:
Is the elctric on?
Is the gas on?
Is the boielr full of water?
Is there 230V ac on pin X or some such?




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

Thanks for all the help, chaps.

So find out how the controls are meant to work and then see if they are
doing it right.

If only I knew what I was doing, I could probably have a bash.

Any of you live near South East London and got time to come round?

Can anyone recommend a book so I can read up and if not fix the
problem myself, at least have enough ammo to work out where the
problem lies.

Boiler's still working by the way, but I'm not going to advance it.

There should be a multi-core cable connected to the boiler. One of
the cores
is the "switched live" (as opposed to a permanent live) connection -
and is
at mains voltage whenever the external control equipment (timer,
thermostats, zone valves) is collectively calling for heat. You will
need a
boiler circuit diagram and a volt meter to be able to answer the
question.

If this signal *is* present, but the boiler isn't lighting, there's a
problem with the boiler itself


Hello, my boiler has just failed again. This is the scenario:
1. hot water comes on at 5 - 6pm - this worked fine
2. Central heating comes on at 7 - 8pm - this failed.

The boiler is "switched live" - I've tested with a multi-meter.
The thing is, the programmer shouldn't now be calling for heat as it's
after 8pm, but the boiler is still "switched live". When I toggle the
mains supply off and then on, I can hear the fan start and the air
pressure switch clicks. Nothing else happens.

Anyone got any ideas? Is it the boiler AND the programmer that are
faulty??

On Thu, 11 Nov 2004 12:50:45 -0800, Chris wrote:

There should be a multi-core cable connected to the boiler. One of
the cores
is the "switched live" (as opposed to a permanent live) connection -
and is
at mains voltage whenever the external control equipment (timer,
thermostats, zone valves) is collectively calling for heat. You will
need a
boiler circuit diagram and a volt meter to be able to answer the
question.

If this signal *is* present, but the boiler isn't lighting, there's a
problem with the boiler itself


Hello, my boiler has just failed again. This is the scenario:
1. hot water comes on at 5 - 6pm - this worked fine
2. Central heating comes on at 7 - 8pm - this failed.

The boiler is "switched live" - I've tested with a multi-meter.
The thing is, the programmer shouldn't now be calling for heat as it's
after 8pm, but the boiler is still "switched live". When I toggle the
mains supply off and then on, I can hear the fan start and the air
pressure switch clicks. Nothing else happens.

Anyone got any ideas? Is it the boiler AND the programmer that are
faulty??

OK if the boiler is running the fan then it is being asked to do something
so the problem is with the boiler.

If you can't hear the ignition clicks then that's now in centre stage.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

In an earlier contribution to this discussion,
Chris wrote:

There should be a multi-core cable connected to the boiler. One of
the cores is the "switched live" (as opposed to a permanent live)
connection - and is at mains voltage whenever the external control
equipment (timer, thermostats, zone valves) is collectively calling
for heat. You will need a boiler circuit diagram and a volt meter to
be able to answer the question.

If this signal *is* present, but the boiler isn't lighting, there's a
problem with the boiler itself


Hello, my boiler has just failed again. This is the scenario:
1. hot water comes on at 5 - 6pm - this worked fine
2. Central heating comes on at 7 - 8pm - this failed.

The boiler is "switched live" - I've tested with a multi-meter.
The thing is, the programmer shouldn't now be calling for heat as it's
after 8pm, but the boiler is still "switched live". When I toggle the
mains supply off and then on, I can hear the fan start and the air
pressure switch clicks. Nothing else happens.

Anyone got any ideas? Is it the boiler AND the programmer that are
faulty??

I've just had a look at the installation manual for a ThermoCompact boiler
on the Vaillant site - but I don't know whether it applies to your exact
model.

If it does, the electrical connections appear to consist of a strip with 9
connections, labelled 7, 8, 9, L,N, (Earth symbol), 3, 4, 5. Is yours like
this?

If so, 7-9 are low voltage, and not used in UK, L, N, and E are
self-explanatory - with L being *permanent* live, even when the boiler isn't
firing. The important one for your investigation is 4 - which is the
"switched live" to which I referred earlier - and which is turned on and off
by the external control gear. When the fault occurs, does connection 4 have
230v on it, or not?

The other thing indicated by the manual is that you have a display panel -
which indicates water temperature when the boiler is running - but displays
a diagnostic message when something fails. Has your boiler got such a panel
and, if so, what does it say?
--
Cheers,
Set Square
______
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I've just had a look at the installation manual for a ThermoCompact boiler
on the Vaillant site - but I don't know whether it applies to your exact
model.

If it does, the electrical connections appear to consist of a strip with 9
connections, labelled 7, 8, 9, L,N, (Earth symbol), 3, 4, 5. Is yours like
this?

Mine is quite an old version and the is wired slightly differently. I
have terminals 1,2,3,4,5.

If so, 7-9 are low voltage, and not used in UK, L, N, and E are
self-explanatory - with L being *permanent* live, even when the boiler isn't
firing. The important one for your investigation is 4 - which is the
"switched live" to which I referred earlier - and which is turned on and off
by the external control gear. When the fault occurs, does connection 4 have
230v on it, or not?

1 and 2 - have a permanent voltage across them
3 and 4, or 3 and 5 (can't remember which) are the "switched live",
and when the prgrammer was calling for heat, there was a voltage
across these terminals too.

The other thing indicated by the manual is that you have a display panel -
which indicates water temperature when the boiler is running - but displays
a diagnostic message when something fails. Has your boiler got such a panel
and, if so, what does it say?

The display panel consists of a water temp gauge and a system pressure
gauge. It doesn't have a diagnostic message, unfortunately. If only
it did.

The boiler has now failed completely which I'm actually quite pleased
about as now my engineer has got a starting point.

I'll let you know what he says.

Thank you and everyone else for their efforts, it's very much
appreciated.

On Thu, 11 Nov 2004 22:02:01 -0000, "Set Square"
wrote:

The other thing indicated by the manual is that you have a display panel -
which indicates water temperature when the boiler is running - but displays
a diagnostic message when something fails. Has your boiler got such a panel
and, if so, what does it say?

Hi,

If it has a microcontroller maybe there is some sort of master reset.

cheers,
Pete.

The night before the morning the engineer was due to come round, the
boiler started working again!

Back to square one.