Revised Honeywell Sundial Plans

[Dave Osborne]

Hello,

We have a wiki page here: -

details of the different arrangements for domestic central heating. I had prepared wiring diagrams for the site and also for download as a pdf: -

I made a transcription error in the wiring diagram for Y-plan which is not obvious and which would cause incorrect operation of the system if implemented. Fortunately, someone spotted the error and posted a note on the wiki.

I have now corrected the error in the Y-plan wiring diagram. If you have previously downloaded the image of the Y-plan wiring diagram or the pdf's (at Rev 1b), then you should discard them and re-download the revised items (at Rev 1c). Please pass on to anybody you you may have emailed the pdf's to.

Thanks to whoever spotted the mistake and to Mr Rumm for updating the the wiki.

Cheers, Dave Osborne

[Roger Mills]

Excellent!

I wonder whether it's worth adding one additional refinement to reflect the way in which many systems are *actually* configured? I'm referring here to pump over-run arrangements. Your diagrams faithfully reproduce the original Honeywell 'plan' details - with the boiler and pump wired in parallel in all cases. However, many (most?) modern systems ain't wired like that, but are wired as follows:

The boiler has several additional terminals - permanent live, plus N, E, L for pump connection, and the terminal shown as L on the diagrams becomes a "switched live" (demand) to distinguish it from permanent live. The pump is then, of course, connected to the boiler's pump terminals rather than as in the diagrams.

[This enables the boiler to control the pump, and to keep it running after the demand has been removed in order to carry away the residual heat].

I would suggest that if you take up this idea, the modified diagrams should be in addition to the original ones rather than replacing them so that, for example, we might have Basic Y-Plan *and* Y-Plan with pump over-run, etc. The schematic for S-Plan (and S+) with pump over-run would also need to include a by-pass circuit.

[ARWadsworth]

Just after printing rev 1b out for laminating as well:-(

An excellent effort despite the earlier small mistake that I missed despite wiring up quite a few Y plans. Far better than any other diagrams I have seen

I love the extra page with the internals of the mid position valve

Well done and thank you

Adam

[Dave Osborne]

Well, I'd be willing to bet that there are many millions of systems out there wired to a classic Sundial plan. Mine is, for one... :-)

However, I'm quite happy to do additional drawings for more modern installation arrangements.

From my limited reading, the following ideas come to mind:-

1. Wiring diagram for S-plus with one and two extra heating zones.
2. Conventional (i.e. not system) boiler with pump-overrun timer (as you have suggested above).
3. Classic Y-plan, S-plan with retro-fitted separate pump overrun timer. (e.g. Broyce Controls M1EDF RS 296-7393).
4. System boiler? I'm kind of assuming that these come with wiring diagrams and have "wiring centres" built in, so the programmer (if external) and the thermostats connect directly to the boiler.
5. Versions of Y, S and S-plus where there is no central timer, just programmable thermostats. Is this even a valid way of wiring a system?

I would need someone or three to commit to assisting with providing suitable source material (including sketches) and/or reviewing and commenting on draft drawings as I am no expert on central heating controls.

Any takers?

DaveyOz

[Dave Osborne]

Thanks Adam. Please see my reply to Roger also.

[ARWadsworth]

That would be good. Zoning of CH is becoming more common. Possible problems would be the way the CH zones are controlled. Some installers use three channel programmers (or extra programmers) and others just use extra room stats that are controlled by just one programmer.

Probably the most common set up now on a new regular boiler. Yes that would be a good one to go for.

Not sure about this one. I have added pump over runs but only because a lack of available cables down to the old boiler and the customer did not want kitchen tiles smashing off the wall etc.

Maybe. But a system boiler usually only needs Permant Live, Neutral, Earth and a Call Live. The pump is taken care of internally by the boiler PCB

It is a valid way of wiring a boiler. Unless someone comes up with a genius "all in one" diagram then I suspect that there would be too many variables to make this a viable option. The system could consist of a mixture of remote and hard wired thermostats and it is not possible to cover all aspects.

If you do not mind hand drawn scanned sketches then no problem.

Adam

[Dave Osborne]

Ok, please feel free to amend existing drawings/wiring diagrams by hand or draw new sketches or whatever is best for you and email them to me.

Cheers, DaveyOz

[Roger Mills]

Yes - although it's not necessarily a *timer* per se. My boiler simply keeps the pump running until the output temperature falls below the boiler stat setting. The important thing is that the pump is controlled by the boiler - using whatever internal logic it sees fit - rather than being connected in parallel with the boiler demand.

Maybe(?) but I don't know how common this is. My impression is that if the boiler *needs* the pump to over-run, it will provide the logic and the connections.

I've not got any experience of these, I'm afraid - but I assume they're simple to wire 'cos most of it will have been done for you.

Unusual I would have thought - because you would normally have a timer of some sort (rather than a programmable stat) for the HW. You could, of course, just have a single channel timer for the HW and connect the programmable room stat(s) directly to the FCU. That would certainly be valid.

I'm more than willing to review and comment. I'm also happy to have a go at amending the existing diagrams - preferably electronically - but that assumes that I have the same tools as those with which you created the diagrams, which may or may not be the case. What *did* you use?

Failing that, I could probably print them, mark them up by hand and then scan them.

[Dave Osborne]

Understood. "Pump Overrun Facility" from mow on!

Good point.

You could, of

OK, I might draw this as an example of an S-plus system.

Well back in August I started in AutoCad cos I'm used to doing drawings in Autocad, but then I decided to use Adobe Illustrator to tart them up and make gifs. However, I ended up largely redoing them in Illustrator and have now dropped AutoCad as an intermediate.

No problem. Whatever works for you.

[Dave Osborne]

Not true, see C-plan. In this arrangement, the boiler and pump are not wired in parallel. The boiler can run without the pump when there is call for hot water but no call for heating.

However, my understanding is that this type of system (C-plan) is deprecated and if you were to replace the boiler, then you would automatically upgrade to fully-pumped and then you would need to change wiring to S-plan and probably implement the boiler overrun as discussed.

[geoff]

In message , Roger Mills writes

What boiler is that ?

[Roger Mills]

Sorry - you're right - it's not *quite* all cases - I overlooked C-Plan systems!

True - but there is still scope for converting a 'conventional' gravity HW/pumped CH system to C-Plan *without* changing the boiler, in order to gain the advantages of HW temperature control and boiler interlock. However, these systems invariably use boilers which *don't* need pump over-run - almost by definition, because the pump doesn't run in HW-only mode, anyway. So, in the case of C-Plan, the existing Honeywell info will suffice without requiring any embellishments.

[Roger Mills]

It's a Mk I Baxi Solo powered flue jobby - c1990 vintage.

[Roger Mills]

I haven't got *any* of them!

Looks like it will have to be knife and fork methods then! Is the email address in your header genuine if I remove the obvious spam-trap?

[Dave Osborne]

Yes, in fact you Adam & John Rumm should have received an email from me. Let me know if your email addresses are not valid.

[geoff]

In message , Roger Mills writes

Ah - simply switched from the stat then, the solo2 the pump overrun would be time, not temp controlled

[Roger Mills]

Yes, that's right. There's an extra set of change-over contacts on the boiler stat which connects the pump either to boiler demand or to permanent live depending on whether the boiler is below or above the set temperature.

Unfortunately, this doesn't always have the desired effect! There are some cases where the demand is cut when the stat is just below the set point, so the pump is immediately cut. The residual heat then sends the temperature up, and the stat switches so that the pump comes on again - but too late to prevent the over-heat stat from tripping. So I have re-engineered mine by using an external timer (intended for bathroom fans) which keeps the pump running for about 4 minutes after the boiler has switched it off - thus avoiding the above problem.

[Roger Mills]

Ah yes, so I have! The address is genuine but - like it says in my sig - I don't look at it very often so I need to be prompted when someone sends an email to it.

I'll respond when I've had a chance to look at it.