Attempting to Fit New Drayton MiTime Wireless Thermostat to French Boiler of Dubious Age

[Neil]

Hi there - my first post, so please forgive me if I wander off track.

We have what is apparently a very simple central heating system (famous last words). No zones, no motorised valves, central heating only, oil-fired Ideal Standard Cadette. This will get replaced when cash-flow allows - maybe next year, as the only thing it really seems to heat is the flue. That's a bit harsh, I guess, it does heat the house but fuel consumption is a bit too high.

Currently, there is a Landis and Gyr Bellman thermostat in the hall and we set this to a lower temperature at night and have to reset to a higher temp in the morning.

We want to have the Drayton MiTime switch the heating on and off at set times and, to this end, I've bought a Drayton MiTime T720R. I understand this is a dual channel controller - at this stage the second channel will not be used and is for future use with a new boiler and, hopefully zoned radiators.

I've wired up a power supply for the programmer unit and arranged for it to be fused, as per the instructions. I don't seem to be able to get a 3 amp fuse in France so there is currently a 2 amp fuse in line with the Drayton.

The current Landis and Gyr thermostat is, I'm assuming, carrying a mains current supplied via the boiler controls. There are two wires from this thermostat that run back to the boiler.

The Drayton programmer for the T720R has two terminals: "CH ON" and "CH OFF". In my naivety, I had hoped that I would simply be able to connect the two wires from the boiler side that go to the Landis and Gyr thermostat to the Drayton "CH ON" and "CH OFF".

However (there's always a however), although I can set the new wireless thermostat to call for heat, the boiler does not start up.

If there's anyone out there who's done this before (I've checked previous posts and, although close, nothing touches exactly on my problem) I would appreciate any thoughts or ideas.

I have the wiring diagrams for the Cadette boiler, if necessary, and also the Installer's Guide for the Drayton. This can also be found here: http://www.draytoncontrols.co.uk/sites/default/files/MiTime%20Pack%201%20(I.%20Guide).pdf

Here's hoping...............

[Gluestick]

Welcome to the forum, Neil.

Quite some time since I played in this bit of the sandbox! [:)]

I must confess to some confusion, here.

You wish to fit two modules: first, a new programmer, with wireless communication to a new matching wireless thermostat? Is this correct?

Therefore, your first step is to work out a suitable connection to enable (switch on and off) the boiler. Now, since it is an oil burner (Chaudiere de fioul), then it has, usually, a separate brûleur, which usually sticks out in the front.

Have a look here:

The large red bit with the black end casing is it. This pumps in the oil, sprays it through an atomising jet and ignites the mixture.

Thus if your new programmer interrupts the mains supply (usually Phase - Live -) to the brûleur then it is either On or Off.

Does your system have a pump? Does it also heat Domestic Hot Water (DHW)? Most older systems didn't, as most French householders, us included, rely on a Ballon(Mains pressure insulated electric water heater operating. on cheap (night) rate.

How was the boiler (Chaudiere) wired in previously? Was there any form of programmer or time switch? Often all that was employed was a simple mains On/Off switch!

Finally, if this is an old system, then I would recommend you arrange for a Chauffagist (Boiler technician) to visit; clean it out and re-set the inlet pressure. Usually should not be too expensive; your oil supplier can usually recommend one. You should then find a marked increase in heat output.

[Neil]

Hi Gluestick - thanks for taking the time to reply.

Yes, the boiler looks more or less the same as the unit shown in your link. There is a circulator, or pump, and the system does not heat the hot water.

Yes, the Drayton unit I'm trying to install comes as a "matched pair". The base unit is a typical programmer where one sets, for example, on and off times. The wireless thermostat is bound to the base unit and communicates, of course, the room temperature where the wireless unit is placed.

The existing system requires two mains connections: one for the boiler and one for the circulator/pump. This was supplied via a switched unit providing fused outlets to the boiler and pump that I've replaced with a switched unit providing three fused outlets to the boiler, pump and the new programmer.

There is currently a two-core wire that runs from the boiler to the Landis and Gyr thermostat - this is the old, brown type square unit with a dial that goes on the wall and which "clicks" when you turn it up to get the central heating to come on by raising the desired temperature. From the boiler wiring diagram I think I'm correct in determining that this current thermostat is "driven" by a mains feed from the boiler.

My understanding is that a thermostat is basically just a switch. I therefore expected that, if I connect the boiler-side of the two-core thermostat wire to the appropriate terminals on the Drayton programmer, I would basically be back to where I started, albeit with the room temperature feedback now arriving via the new wireless thermostat.

I am not switching, or in any way altering, the mains feed to the boiler or pump.

Does that help to clarify?

Thanks again for taking an interest.........Neil

[Gluestick]

[quote user="Neil"]

 The existing system requires two mains connections: one for the boiler and one for the circulator/pump. This was supplied via a switched unit providing fused outlets to the boiler and pump that I've replaced with a switched unit providing three fused outlets to the boiler, pump and the new programmer.[/quote]

You should switch both the boiler and the pump from the new programmer, I believe. Since there is little point in turning off the boiler and leaving the pump running.

Usually, the thermostat feeds both. Are you saying the thermostat only switches the boiler, originally?

A rough schematic circuit of the original installation would be most helpful: first thing I do, before changing anything! And mark each and every wire...

[quote]There is currently a two-core wire that runs from the boiler to the Landis and Gyr thermostat - this is the old, brown type square unit with a dial that goes on the wall and which "clicks" when you turn it up to get the central heating to come on by raising the desired temperature. From the boiler wiring diagram I think I'm correct in determining that this current thermostat is "driven" by a mains feed from the boiler.[/quote]

Doesn't need "Driving", Neil: it a simple mechanical thermostat which acts as a switch, normally enabling a phase (live) feed to the boiler. The click is when the micro-switch turns off or on. Those older mechanical thermostats relied upon a Bi-Metal strip which bent according to ambient temperature changes: cold, moves one way to enable the micro-switch; warm, bends the other way, simple as that.

[quote]My understanding is that a thermostat is basically just a switch.[/quote]

Sort of; these days a thermostat is based on a Thermistor, usually: these come in two flavours: PTC and NPC. Which means Positive Temperature Coefficient and reverse. Since they are a sold state device, then they require some logic circuitry to function; usually TTL = Transistor -Transistor Logic. Also depends on whether, finally, they are intended to switch resistive or inductive loads. Confusing, huh?

What I would do, is rather simple; I adore simple!

Step One: check to see which of the old thermostat wires is live.

Step Two: The new programmer no doubt has one of those nasty plug in bases, where the wiring goes to the base and the programmer sort of plugs in. Run wires from terminals 2 and 4 into a n insulated terminal block. The bigger the block the better. If mains is on and you have already connected to the N and L terminals, then the programmer should function. Select CH on. Then with a neon screwdriver or circuit tester, check to see which of 2 and 4 is live. Tgen select CH Off and ensure the terminal (2 or 4) is dead.

Connect the RETURN wire from the old 'stat (i.e. the Non-Live Wire) to the terminal (2 or 4) which becomes live when the programmer has been set to CH On.

(P.S. I am looking at the wiring diagram schematic of your unit as I write this).

Caution! Take great personal care when dealing with live mains electricity!!

[Neil]

Hi again - thank you for your perseverance.

Under the current setup, the pump runs continuously, whether the boiler is on or off. I agree with the KISS principle, so had not considered trying to switch the pump off via the thermostat. From what I've read, and you have seen that I'm no expert, there is some benefit in continuing to circulate the water through the rads even though the thermostat is no longer calling for heat - at least the residual warmth of the circulating water is being put to use.

When I've been talking of power being switched to the boiler, pump and new programmer, perhaps what has not been clear is that I'm trying to describe a simple isolating switch. So, power comes via a circuit breaker on the main house panel, then to the isolating switch (i.e. a simple On/Off switch rather than an amp-rated circuit breaker) then to the boiler, pump and programmer. This was as per the original setup and I assume this was simply a way to (a) isolate the central heating equipment from the rest of whatever is on that circuit breaker (should only be the boiler/pump, I hear you say , but isn't - there are also other sockets) and (b) enable a lower fuse rating to be applied across the boiler and pump. I swapped the switch with the two fused outlets for one with three. In winter, the switch stays on and the pump runs continuously with the boiler coming on and off as determined by the room stat.

To labor the point, in the existing arrangement, when the desired temperature is reached, the boiler cuts off but the pump continues to run - we've only been in the house for a year but I'm guessing it's always been this way.

I'll supply a wiring schematic tomorrow and will also try what you suggest. Don't worry, I'm very careful with any voltage above 1.5

Thanks for your help and I'll provide feedback soonest.

Neil

[Gluestick]

[quote user="Neil"]Hi again - thank you for your perseverance.

Under the current setup, the pump runs continuously, whether the boiler is on or off. I agree with the KISS principle, so had not considered trying to switch the pump off via the thermostat. From what I've read, and you have seen that I'm no expert, there is some benefit in continuing to circulate the water through the rads even though the thermostat is no longer calling for heat - at least the residual warmth of the circulating water is being put to use.

[/quote]

All provided the rads are connected correctly with a feed and return circuit (Some early systems simply fed the rads in series via one circuit only! [:-))] ), then as the rads are fed via "risers" to each rad, then a natural Thermo-Syphon should continue to circulate hotter water warmed by the boiler casing. You can try both.

When it is all working correctly, I will explain - remind me if I forget! - how to "Balance" each rad in order to achieve optimal heating.

[quote]I'll supply a wiring schematic tomorrow and will also try what you suggest.[/quote]

Very good and essential in this case!

[quote]Don't worry, I'm very careful with any voltage above 1.5[/quote]

Sounds like an old close chum of mine; he was so scared of electricity, he even used to wear rubber gloves to change his torch batteries!

[:D]

[Neil]

Hi again Gluestick

Well, I'm not sure if you'll see these pictures - the forum technical support for Photobucket may be a bit out of step with its current manifestation, but here goes:

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20As20Was_zpsv2osnm22.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20Current_zpsmet2y7qa.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20Boiler20and20Stat_zpskhrluy26.jpg[/IMG]

You'll see that the original wiring, in terms of colour coding, is a bit of a B##g$s Muddle. I understand this may be "normal" but always a question as to whether to carry on with the convention in use or try and sort it out............

Anyway, by the time the cable from the L&G thermostat reaches the boiler there's a brown and blue in the 2-core cable (it changes colours along the way, of course). The blue thermostat wire is live.

Moving on to the new programmer, when CH is on terminal 4 of the programmer is live.

When CH is off, terminal 2 of the programmer is live.

This is as measured across the terminals and earth.

I did not complete the last step in your previous post, i.e. connecting the return (non-live) wire (now understood to be the brown) to terminal 4 (now understood to be live when CH is on). I do not understand what to to do with the remaining thermostat (blue) wire - just terminate it?

Regards........Neil

[Neil]

Hmmm...........I see the three pictures when I preview the post but not after I've actually POSTed.

Let me know if you see them please...........Neil

[Gluestick]

[quote user="Neil"]Hi again Gluestick

Well, I'm not sure if you'll see these pictures - the forum technical support for Photobucket may be a bit out of step with its current manifestation, but here goes:

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20As20Was_zpsv2osnm22.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20Current_zpsmet2y7qa.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/CH20Boiler20and20Stat_zpskhrluy26.jpg[/IMG]

You'll see that the original wiring, in terms of colour coding, is a bit of a B##g$s Muddle. I understand this may be "normal" but always a question as to whether to carry on with the convention in use or try and sort it out............

Anyway, by the time the cable from the L&G thermostat reaches the boiler there's a brown and blue in the 2-core cable (it changes colours along the way, of course). The blue thermostat wire is live.

Moving on to the new programmer, when CH is on terminal 4 of the programmer is live.

When CH is off, terminal 2 of the programmer is live.

This is as measured across the terminals and earth.

I did not complete the last step in your previous post, i.e. connecting the return (non-live) wire (now understood to be the brown) to terminal 4 (now understood to be live when CH is on). I do not understand what to to do with the remaining thermostat (blue) wire - just terminate it?

Regards........Neil[/quote]

Neil: everyone ought now to be able to see the schematics.

I will revert shortly, as I would like again, to look carefully at the Drayton schematic.

Yes it is a crow's nest...

[+o(]

[Gluestick]

Neil: a couple ( I think? Been long day and I now rather braindead).

1.    You tested the programmer by assessing terminals 2 and 4 to Earth? Why not Neutral?

It is normal to check voltage between Phase (Live) and Return (Neutral).

2.    What is the reverse position, please? i.e. potential voltage between Neutral and Terminals 2 and 4 in the "Off" condition?

Conclusion: All provided terminal 4 (Marked on legend CH ON) is dead when the programmer is OFF, then all you need to do is to connect the old return wire from the L&G Thermostat (Brown to the brûleur) to terminal 4 and the boiler should fire up.

Logic: the Blue Wire feeds the live connection to the old Thermostat. The 'Stat acts as a switch, and powers up the jolly old brûleur, which is then enabled. All that has happened is the previous switching arrangement (mechanical) is now managed by the programmer, electronically and probably by micro-relays; (That said they might well be switched by power transistors and/or thyristors. Dunno; would have to examine the pcb.).

Wiring: personally, I would wish to tidy this up, PDQ! All feeds in surface mounted conduit. and connect those two pesky sockets elsewhere!

[Neil]

Hi again - thanks once again for staying with this.

I understand the logic and will re-test and provide feedback tomorrow.

Nothing can go wrong, right?

Neil

[Gluestick]

[quote user="Neil"]Hi again - thanks once again for staying with this.

I understand the logic and will re-test and provide feedback tomorrow.

Nothing can go wrong, right?

Neil[/quote]

If all is as described, Neil, then no. After all, what you are doing is to provide, via the programmer, a live feed to the jolly old brûleur: which is thereby enabled and should fire up.

Thereafter, the wireless thermostat will provide its own intervention, remotely and cause the live programmer feed to turn on and off on demand.

[Neil]

Me again - and a very frustrated me at that.

The short story is that connecting the brown wire of the thermostat cable from the boiler side to T4 of the programmer blows the 2 amp fuse. You'll remember that I'm having to use a 2 amp fuse in the place of the Drayton-recommended 3 amp fuse.

Readings taken today, now measuring across neutral, not earth as before:

With heating on, T4 shows 240V and T2 shows 40V

With heating off, T2 shows 240V and T4 shows 48V

I also re-measured voltage and current across the old L&G thermostat:

With heating off, blue shows live at 240V and 1.6 amps, brown shows 0V/0 amps.

With heating on, blue and and brown both show 0V/0 amps.

I'm also attaching, in case this helps, the boiler wiring diagrams.

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/Wiring20Part201_zpsqcoxx5g3.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/Wiring20Part202_zpsf04aa3wg.jpg[/IMG]

[IMG]http://i350.photobucket.com/albums/q422/_NeilMiller/Central%20Heating/Customer20Connections_zpsd72vikwn.jpg[/IMG]

Let me know if I've yet driven you towards suicide and I'll desist......Neil

[Gluestick]

Neil.

Perhaps the critical key here, is the simple fact your L&G thermostat reads zero volts and amps (no drain or residual current) when off. and 230/40 V AC when on.

Therefore, via a fuse (5 Amp ideally, since the initial "Surge Current" - pump motor -  may well blow a 3 amp jobby),  try connecting a phase (live) feed to the wire going into the Brûleur and see if the boiler fires up.

If it then does, ergo summat amiss with your programmer, logically.

Suggest you contact Drayton tech services and request some guidance. No way there should be voltage on terminal 4 if it is off.

Will ponder some more tomorrow, as have managed to copy and paste the boiler wiring schematics.

[Neil]

Many thanks Gluestick

I have emailed Drayton, a couple of days back, but no reply. I may be out tomorrow but will try and follow up with them and will get back to you.

Many thanks for your perseverance again.......Neil

[Gluestick]

Neil:

Have PMd you.

[Neil]

OK, so this is to anyone trying to follow this post to understand whether an outcome was achieved and a resolution found.

After several offline discussions with Gluestick, who provided, with much patience, outstanding advice and counsel, it was concluded that the Drayton MiTime was a central heating controller rather than a simple thermostat replacement.

This means that the Drayton MiTime will have to go on the shelf until such time as a new boiler is installed and I will then achieve programmed control of temperature, boiler on-off times and appropriate switching of the circulation pump, etc.

In the meantime, if I feel brave enough, I may look at buying a programmable thermostat to achieve what I want.

My thanks to Gluestick once again.