Hi

I need some advice on a problem I'm having having with my central
heating.

First off, my existing setup is a Baxi Solo 70/4 PF in an S-PLan+
arrangement. It has/had a bypass that consisted of 1' of 15mm pipe
bridging the flow and return with a Gate valve to control the flow.

I tried to turn the thermostat on the boiler up to increase the
temperature of the radiators in an attempt to get the house up to
temperature. This works fine until the room thermostat clicks off (or
the ch timer cuts off) then all hell breaks loose. Obviously the water
is kettling in the boiler and this results in all the banging. Easy
enough so far. Assuming there was a pump overrun on the boiler to cope
with this I started messing about with the gate valve to no great
effect. I then decided that the bypass wasn't dumping enough heat so
re-routed a towel radiator (with no TRV) in the bathroom to act a
bypass. Still no joy. I then realised that the pump wasn't actually
overrunning at all! A quick google and I had convinced myself that this
boiler has a timed overrun of 7mins (how I came up with that, don't
ask). So I decided this was knackered and not wanting to bugger about
with things too much at this time of year, decided pipe thermostat
wired in parallel to the pump would be the answer.

Duly fitted and everything seemed great, cranked up the boiler
thermostat, set the pipe thermostat and left it too it. Result was a
nice roasty-toasty house and no banging/thumping when the room
thermostat clicked off.

Now you've probably guessed by now that I'm not writing this to tell
you that I fixed it!

When the room thermostat clicks off, the 2-port valve closes and the
boiler shuts down. The pipe thermostat keeps the pump running until the
temperature drops. However, before the pipe thermostat cuts off, the
boiler springs back to life heating the water back up again and so it
goes on. SWMBO likes the bathroom to be warm but we've got an impromptu
sauna now So I've put the boiler thermostat back down to position 2
and turned the pipe thermostat setting up and am back to where I
started.

A further search resulted in finding the manual for the boiler (Baxis
spares partner site, doh) It turns out the boiler thermostat is what
controls the overrun and following the fault finding diagram would
suggest that replacing it should solve all my ills. I've no problem
doing this but wonder if this will just re-introduce the cycling
problem and there is something more fundemental going on.

Should the boiler not have some sort of interlock that stops it from
firing when there is no actual heating load. I'd noticed it coming on
every now and again in the summer but thought nothing of it at the
time.
Sorry for the long post but its a slow day at work!

Cheers,

Mark.

Big snip!

oh and how do I stop my email address being visible to everyone (I'm
accessing via Google Groups)
Too late now I suppose (It's not my main account anyway)

Mark

In an earlier contribution to this discussion,
wrote:

Hi

I need some advice on a problem I'm having having with my central
heating.

First off, my existing setup is a Baxi Solo 70/4 PF in an S-PLan+
arrangement. It has/had a bypass that consisted of 1' of 15mm pipe
bridging the flow and return with a Gate valve to control the flow.

I tried to turn the thermostat on the boiler up to increase the
temperature of the radiators in an attempt to get the house up to
temperature. This works fine until the room thermostat clicks off (or
the ch timer cuts off) then all hell breaks loose. Obviously the water
is kettling in the boiler and this results in all the banging. Easy
enough so far. Assuming there was a pump overrun on the boiler to cope
with this I started messing about with the gate valve to no great
effect. I then decided that the bypass wasn't dumping enough heat so
re-routed a towel radiator (with no TRV) in the bathroom to act a
bypass. Still no joy. I then realised that the pump wasn't actually
overrunning at all! A quick google and I had convinced myself that
this boiler has a timed overrun of 7mins (how I came up with that,
don't ask). So I decided this was knackered and not wanting to bugger
about with things too much at this time of year, decided pipe
thermostat wired in parallel to the pump would be the answer.

Duly fitted and everything seemed great, cranked up the boiler
thermostat, set the pipe thermostat and left it too it. Result was a
nice roasty-toasty house and no banging/thumping when the room
thermostat clicked off.

Now you've probably guessed by now that I'm not writing this to tell
you that I fixed it!

When the room thermostat clicks off, the 2-port valve closes and the
boiler shuts down. The pipe thermostat keeps the pump running until
the temperature drops. However, before the pipe thermostat cuts off,
the boiler springs back to life heating the water back up again and
so it goes on. SWMBO likes the bathroom to be warm but we've got an
impromptu sauna now So I've put the boiler thermostat back down to
position 2 and turned the pipe thermostat setting up and am back to
where I started.

A further search resulted in finding the manual for the boiler (Baxis
spares partner site, doh) It turns out the boiler thermostat is what
controls the overrun and following the fault finding diagram would
suggest that replacing it should solve all my ills. I've no problem
doing this but wonder if this will just re-introduce the cycling
problem and there is something more fundemental going on.

Should the boiler not have some sort of interlock that stops it from
firing when there is no actual heating load. I'd noticed it coming on
every now and again in the summer but thought nothing of it at the
time.
Sorry for the long post but its a slow day at work!

Cheers,

Mark.

If your Baxi Solo is like mine, the pump over-run is controlled by the main
thermostat - with an extra set of change-over contacts. When the boiler is
below stat temperature, the pump is connected to switched live - so only
runs when there is a demand from the room stat/zone valve or whatever. When
the boiler is above stat temperature, the pump is connected to permanent
live - so it runs for as long as it takes to cool the boiler down - rather
than for a fixed time.

It sounds to me as if your system has never been wired correctly. The boiler
needs a permanent live from the heating system FCU, and a switched live from
volt-free contacts in the zone valves, (which are all connected in
parallel). The pump must be connected ONLY to the boiler's pump connection.

It also sounds as if you have compounded the problem by fitting a pipe stat.
If you implement a pump over-run with a pipe stat, it *must* have
changeover-contacts - with COM connected to the pump (and no other pump
connection) NC connected to boiler switched live and NO to permanent live.
Any other arrangement will probably bring the boiler on when the pump is
running in over-run mode - which is what you appear to have.
--
Cheers,
Set Square
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I'll take out the Pipe Stat. I think the COM/NC/NO arrangement is how I
have it but who knows it was done in a bit of a rush while wife and
weans were out.

So, the best course of action is to replace the boiler thermostat
first, see if that fixes my all my problems, failing that check out the
original wiring? I know that sounds obvious but I'm looking for minimum
disruption. (I can do without the HW side- immerser and electric shower
- but not the CH side at this time of year)
Any good, i.e. cheap, suppliers of Baxi parts?

Mark

In an earlier contribution to this discussion,
pollocmc wrote:

I'll take out the Pipe Stat. I think the COM/NC/NO arrangement is how
I have it but who knows it was done in a bit of a rush while wife and
weans were out.

So, the best course of action is to replace the boiler thermostat
first, see if that fixes my all my problems, failing that check out
the original wiring? I know that sounds obvious but I'm looking for
minimum disruption. (I can do without the HW side- immerser and
electric shower - but not the CH side at this time of year)
Any good, i.e. cheap, suppliers of Baxi parts?

Mark

Why do the think that the boiler stat is faulty. Does it turn the burner on
and off ok to control the output temperature? The pump is controlled by an
additional set of contacts within the *same* thermostat - so just that
additional set would have to be faulty. Possible but unlikely.

My guess - as I said before - is that it's never been connected up properly.
Sort that, and it will probably work!

If you do need spares, have a word with Geoff at
http://www.cetltd.com/default.asp
--
Cheers,
Set Square
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On Wed, 05 Jan 2005 09:02:28 -0800, pollocmc wrote:

I'll take out the Pipe Stat. I think the COM/NC/NO arrangement is how I
have it but who knows it was done in a bit of a rush while wife and
weans were out.

So, the best course of action is to replace the boiler thermostat
first, see if that fixes my all my problems, failing that check out the
original wiring? I know that sounds obvious but I'm looking for minimum
disruption. (I can do without the HW side- immerser and electric shower
- but not the CH side at this time of year)
Any good, i.e. cheap, suppliers of Baxi parts?


The pump should be connected to the pump terminals on the boiler.
Sometime the installers simply put the pump in parallel with the boiler
demand.

--
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

Why do the think that the boiler stat is faulty

No good reason other than following the fault finding diagram has a
branch that suggests that you can have an operational (ie controls
temperature) thermostat but the pump does not overrun. The solution
they give for this is to replace the thermostat.

I take on board what you say though. And if fixing the wiring sorts it
out then I have the cheapest solution of all!

I've found a supplier of what I think is the replacement thermostat (it
seems to have been superceded by a newer model) and it's only =A318 so
not the end of the world anyway but thanks for the link. I'll file it
for future reference.=20

Mark

In an earlier contribution to this discussion,
pollocmc wrote:

Why do the think that the boiler stat is faulty

No good reason other than following the fault finding diagram has a
branch that suggests that you can have an operational (ie controls
temperature) thermostat but the pump does not overrun. The solution
they give for this is to replace the thermostat.

Yes, but the fault-finding chart assumes that it has been installed
correctly and has subsequently gone wrong. It sounds as if yours has *never*
worked properly. As Ed has suggested, the pump is probably connected to the
switched live and not to the specific pump terminals.

As I said earlier, the boiler needs a switched live *and* a permanent live.
Without a permanent live, pump over-run won't work - because the pump needs
a source of supply whenever the boiler demand has been removed but the
boiler is still too hot. So check *all* the wiring.
--
Cheers,
Set Square
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Fairy nuff, I think that is what I was saying I would do but maybe I
missed out the check wiring *first* then go looking for other problems.
It's unlikely I'll get a chance to look at it before the weekend so
I'll post an update after that. I think my first task will be to label
the mess of cables in situ before trying to rearrange them. I'm
generally a messy bugger but I like wiring to be neat with nice diagram
beside it to show what's going on.

Mark.

In message .com,
pollocmc writes

Big snip!

oh and how do I stop my email address being visible to everyone

Cease posting ?

--
geoff

In message , Set Square
writes

My guess - as I said before - is that it's never been connected up properly.
Sort that, and it will probably work!

If you do need spares, have a word with Geoff at
http://www.cetltd.com/default.asp

If it had been a solo 2, the pump overrun is on the pcb, and is a
reasonably common fault. The Solo mk 1 has a much more primitive pcb and
doesn't control the pump

--
geoff

In an earlier contribution to this discussion,
raden wrote:

In message , Set Square
writes

My guess - as I said before - is that it's never been connected up
properly. Sort that, and it will probably work!

If you do need spares, have a word with Geoff at
http://www.cetltd.com/default.asp

If it had been a solo 2, the pump overrun is on the pcb, and is a
reasonably common fault. The Solo mk 1 has a much more primitive pcb
and doesn't control the pump

I assume you mean that the *PCB* doesn't control the pump on the Mk I?

The *boiler* still controls the pump via an extra change-over contact on the
main stat which connects the pump either to switched live or permanent live
depending on whether the water temperature is below or above the stat
setting.

--
Cheers,
Set Square
______
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In message , Set Square
writes
In an earlier contribution to this discussion,
raden wrote:

In message , Set Square
writes

My guess - as I said before - is that it's never been connected up
properly. Sort that, and it will probably work!

If you do need spares, have a word with Geoff at
http://www.cetltd.com/default.asp

If it had been a solo 2, the pump overrun is on the pcb, and is a
reasonably common fault. The Solo mk 1 has a much more primitive pcb
and doesn't control the pump

I assume you mean that the *PCB* doesn't control the pump on the Mk I?

Yes I did


The *boiler* still controls the pump via an extra change-over contact on the
main stat which connects the pump either to switched live or permanent live
depending on whether the water temperature is below or above the stat
setting.


Yes - in other words, I wouldn't be able to help by sending him a PCB

--
geoff

In an earlier contribution to this discussion,
raden wrote:

In message , Set Square
writes
In an earlier contribution to this discussion,
raden wrote:

In message , Set Square
writes

My guess - as I said before - is that it's never been connected up
properly. Sort that, and it will probably work!

If you do need spares, have a word with Geoff at
http://www.cetltd.com/default.asp

If it had been a solo 2, the pump overrun is on the pcb, and is a
reasonably common fault. The Solo mk 1 has a much more primitive pcb
and doesn't control the pump

I assume you mean that the *PCB* doesn't control the pump on the Mk
I?

Yes I did


The *boiler* still controls the pump via an extra change-over
contact on the main stat which connects the pump either to switched
live or permanent live depending on whether the water temperature is
below or above the stat setting.


Yes - in other words, I wouldn't be able to help by sending him a PCB

I was pretty sure that was what you meant, but felt that "The Solo Mk I . .
.. doesn't control the pump" could be misinterpreted by some people.

--
Cheers,
Set Square
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