Replacing old Honeywell thermostat with Honeywell 907
Kostas Kavoussanakis
Hi,
I would like to replace my old (80s) Honeywell room thermostat with
the 907. It's a very common model.
On the old thermostat there are 5 terminals (top to bottom): 5 2 3 4
1. Of these, 2 (Neutral), 3 (Switch Live) and 1 (Live) are connected.
I understand that the 907 only accepts two wires.
Is my installation compatible with the 907? The installation manual
suggests current needs to by <8A; how does one check that?
http://europe.hbc.honeywell.com/products/pdf/en0h8547uk07r0906.pdf
Am I right that this a DIY job? I know I need to switch the boiler off
at the mains and drop the fuse while the wife and kids are out
shopping :-)
Thanks,
Kostas
John
"Kostas Kavoussanakis" <kavo...@epcc.ed.ac.uk> wrote in message
news:Pine.SOC.4.64.0710222214450.3969@r3000...
You will only need "Live" and "Switched Live". Tape up the neutral as it is
not needed as the thermostat is electronic. Don't worry about the 8 amp
aspect unless you are switching electric heating. It means less than 8
amps - and I guess your boiler has a 5 amp fuse.
Roger Mills
Kostas Kavoussanakis <kavo...@epcc.ed.ac.uk> wrote:
> Hi,
>
> I would like to replace my old (80s) Honeywell room thermostat with
> the 907. It's a very common model.
>
> On the old thermostat there are 5 terminals (top to bottom): 5 2 3 4
> 1. Of these, 2 (Neutral), 3 (Switch Live) and 1 (Live) are connected.
>
> I understand that the 907 only accepts two wires.
>
It actually *accepts* 3 - but you only need and *must* only use 2.
According to the diagram in the document you sited, the three are:
A: Common - (Use the Live from the old stat)
B: Call for heat - (Use the Switched Live from the old stat)
C: Heating Satisfied - Do not - repeat DO NOT - connect anything to that.
Your old neutral wire is not required. Disconnect it and tape it off safely.
DO NOT connect it to anything.
> Is my installation compatible with the 907? The installation manual
> suggests current needs to by <8A; how does one check that?
>
You have to make sure that you're not asking it to switch more than 8 amps.
If you're simply switching the boiler and pump and/or a motorised valve, all
of those together are likely to take less than 5 amps, probably no more than
3 - but check the spec of all the relevant equipment.
> http://europe.hbc.honeywell.com/products/pdf/en0h8547uk07r0906.pdf
>
> Am I right that this a DIY job? I know I need to switch the boiler off
> at the mains and drop the fuse while the wife and kids are out
> shopping :-)
>
Your last question worries me! It's a simple job - well within the scope of
a *competent* DIY-er - but the fact that you had to ask, and couldn't work
it out from the Honeywell literature - not to mention being uncertain as how
to isolate it when working on it - makes me wonder whether maybe you should
be getting some professional help.
Also, it's a moot point whether it's notifiable under the dreaded Part P -
since central heating controls seem to come within its scope. I'm not sure
how convincingly you could argue that it's a 'like for like' replacement.
--
Cheers,
Roger
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Kostas Kavoussanakis
Thank you John and Roger for the quick answer.
On Mon, 22 Oct 2007, Roger Mills wrote:
> In an earlier contribution to this discussion,
> Kostas Kavoussanakis <kavo...@epcc.ed.ac.uk> wrote:
>
>> I would like to replace my old (80s) Honeywell room thermostat with
>> the 907. It's a very common model.
<snip>
>> Am I right that this a DIY job? I know I need to switch the boiler
>> off at the mains and drop the fuse while the wife and kids are out
>> shopping :-)
>
> Your last question worries me! It's a simple job - well within the scope of
> a *competent* DIY-er - but the fact that you had to ask, and couldn't work
> it out from the Honeywell literature - not to mention being uncertain as how
> to isolate it when working on it - makes me wonder whether maybe you should
> be getting some professional help.
Thanks for your concern; what's uncertain about dropping the fuse? :-)
Sure, I will check for current at the terminals as well, isn't that
standard?
The reason why I felt compelled to ask if it's DIY was the quote I got
from my gasman for this replacement: 70 pounds. Also, the standard set
of questions from Honeywell mentions a sub-base as a possibility; I am
not sure how that is defined, so I thought this could be an issue. In
general I thought I had underestimated its complexity.
> Also, it's a moot point whether it's notifiable under the dreaded Part P -
> since central heating controls seem to come within its scope. I'm not sure
> how convincingly you could argue that it's a 'like for like' replacement.
That's important to me: who does one ask? My case would be that it's
"like for like" in the sense that the new thermostat performs the same
electrical task; it just does it in a internally different way.
Thanks!
Kostas
TheScullster
"Kostas Kavoussanakis" wrote
>> Also, it's a moot point whether it's notifiable under the dreaded Part
>> P -
>> since central heating controls seem to come within its scope. I'm not
>> sure
>> how convincingly you could argue that it's a 'like for like' replacement.
>
> That's important to me: who does one ask? My case would be that it's "like
> for like" in the sense that the new thermostat performs the same
> electrical task; it just does it in a internally different way.
>
According to the Pocket Guide 8 (from NICEIC July 2006), "power or control
wiring for a ***new*** central heating system" is notifiable.
This would imply that repairs/replacement of elements of an existing system
is not notifiable and therefore simply needs to meet the requirements of
BS7671.
Phil
Roger Mills
Kostas Kavoussanakis <kavo...@epcc.ed.ac.uk> wrote:
> Thank you John and Roger for the quick answer.
>
>
> Thanks for your concern; what's uncertain about dropping the fuse? :-)
> Sure, I will check for current at the terminals as well, isn't that
> standard?
>
You *should* have an FCU (fused connection unit) which feeds the whole of
the heating system. Turning that off will isolate the heating system without
affecting anything else in the house. But it's always a good idea to check
for *voltage* on anything you're likely to touch, even when you think you've
isolated it. You'll need a voltmeter with a 300v AC range for this - don't
rely on neon screwdrivers!
> The reason why I felt compelled to ask if it's DIY was the quote I got
> from my gasman for this replacement: 70 pounds. Also, the standard set
> of questions from Honeywell mentions a sub-base as a possibility; I am
> not sure how that is defined, so I thought this could be an issue. In
> general I thought I had underestimated its complexity.
>
The only 'complexity' is in understanding the function of each wire, and
being able to work out what to connect to what when the new unit is not
identical to the old one. A common problem is that some people feel
compelled to connect the old neutral wire to something - and end up
connecting it to the only spare terminal, which is 'Heating Satisfied' (C in
your case). The result is that when the house gets up to temperature and the
stat switches, they then have a dead short between live and neutral -
causing a loud, potentially expensive, bang!
>> Also, it's a moot point whether it's notifiable under the dreaded
>> Part P - since central heating controls seem to come within its
>> scope. I'm not sure how convincingly you could argue that it's a
>> 'like for like' replacement.
>
> That's important to me: who does one ask? My case would be that it's
> "like for like" in the sense that the new thermostat performs the same
> electrical task; it just does it in a internally different way.
>
Have a look at
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADP_2006.pdf If you can
wade through the treacle, you can probably find evidence to support the view
that changing a stat is *not* notifiable. [I wasn't sure when I posted
earlier, but it looks fairly safe from that document].
Kostas Kavoussanakis
> In an earlier contribution to this discussion,
> Kostas Kavoussanakis <kavo...@epcc.ed.ac.uk> wrote:
>
>> Thank you John and Roger for the quick answer.
>>
>>
>> Thanks for your concern; what's uncertain about dropping the fuse? :-)
>> Sure, I will check for current at the terminals as well, isn't that
>> standard?
>>
> You *should* have an FCU (fused connection unit) which feeds the whole of
> the heating system. Turning that off will isolate the heating system without
> affecting anything else in the house.
Yes, that's the fuse I intend to drop out of its housing, so as to
also check its rating; if it's under 8 I am laughing.
> But it's always a good idea to check
> for *voltage* on anything you're likely to touch, even when you think you've
> isolated it. You'll need a voltmeter with a 300v AC range for this - don't
> rely on neon screwdrivers!
Thanks for this, I was indeed planning to check with a filament (I
think it is) screwdriver.
> identical to the old one. A common problem is that some people feel
> compelled to connect the old neutral wire to something - and end up
> connecting it to the only spare terminal, which is 'Heating Satisfied' (C in
> your case). The result is that when the house gets up to temperature and the
> stat switches, they then have a dead short between live and neutral -
> causing a loud, potentially expensive, bang!
Noted, this was made clear to me.
> Have a look at
> http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADP_2006.pdf If you can
> wade through the treacle, you can probably find evidence to support the view
> that changing a stat is *not* notifiable. [I wasn't sure when I posted
> earlier, but it looks fairly safe from that document].
Thanks, I have a friendly local spark whom I can ask as well (not the
one who gave me the 70 quid quote :-)).
Kostas
Kostas Kavoussanakis
Folks,
Just to let you know that, thanks to your valuable advice, I have now
replaced the old thermostat with the 907. For the benefit of anyone
contemplating to do the same, here is the process I followed:
I switched off the boiler at its fused switch and removed that fuse. I
checked it was below 8A. I then removed the external casing of the old
thermostat and tested that there was no voltage down to 10V AC at the
terminals. Although it's pretty standard, I noted which colour wire
corresponded to which type (Live, Neutral, Switched-Live), then
disconnected them from the old thermostat and dropped its base.
At this stage I only had three wires and the box on the wall. I
isolated Neutral using a connector, then wrapping the connector with
electrical tape. (My initial intention was to use heat-shrink sleeve,
but I could not readily source it.) I screwed the base of the 907 on
the wall, then connected the Live to terminal A, and Switched-Live to
terminal B of the base, as per the instructions. The rest was as per
instructions. I switched on the boiler at its fused box, then tested
that the thermostat drives the boiler (actually I think it drives the
pump in my case, but never mind) on and off.
I like the new thermostat and am well pleased that I did it myself, if
I may say so :-)
With a little help from my friends, that is! Thanks again.
Kostas