Myson MEP2c Wiring Question

[JunglieD]

Hi All - first time poster so would be grateful for your thoughts on this. I've just moved into a 2011 property with a Myson MEP2c dual channel programmer. There are 2-zones to the heating; upstairs (operated by a Myson MRT1 thermostat) and downstairs (operated by a Myson MPRT programmable thermostat). All heating and hot water systems work effectively and have been serviced today incidentally but there is one anomaly that is niggling me (regrettably I wasn't present to ask the engineer the question):

- The Hot Water in my home is annoyingly set and controlled using the 'Heating' side of the MEP2c!! This was explained to me by the previous owner and he couldn't explain why. But yes, the hot water for my home responds beautifully to the settings entered in the 'Heating' side. The 'Hot Water' side appears to have no function whatsoever and it is left in the Off position permanently (heating works by zone from the respective thermostat).

Photo 1 shows the wiring to the MEP2c mounting plate:

Photo 2 shows the back of the MEP2c programmer:

I'd be grateful for your 2-pennies worth for what I can do to get my Hot Water controlled by the 'Hot Water' 'side' of this Controller - and finally relax my OCD about this!

Best Wishes,

David

 

[Registered Gas Man]

From what I can tell the clock is wired so that HW (3) is wired to be permanently on. Does one of the Brown/Live cables go direct from L > 3?. Picture isn't clear.

 

[JunglieD]

Hi RGM - thanks for your reply. Below is a (hopefully) better photo of the wiring:

Ultimately - Yes, one of the Brown cables goes direct from L > 3 (the 5th cable from left as you look at the photo). All others come from behind the wall...

Now this is clarified, could you expand on why this may be the case and if I can make a simple change to get it so the Hot Water is controlled from the 'Hot Water' side and not the 'Heating' side?

 

[Hot&Cold]

I've just moved into a 2011 property with a Myson MEP2c dual channel programmer.

seems the previous occupiers were prepared to put up with the quirky wiring set up,

To get the programmer switching correctly the wiring needs alterations in the programmer and most probably the wiring centre a heating tech could sort it out.

do you really need the programmable stat for downstairs zone ?

 

[stem]

As has been pointed out, the terminal 3 has indeed been connected to a permanent live. Depending on the design of the wiring / components inside the programmer, this may be feeding back through the internal switches so that one supplies the other. In any event, the two terminals would be linked internally when the hot water was set to 'on' anyway.

Remove the link between L and 3 as it doesn't appear to be serving any useful function, and move the black wire from terminal 4 to terminal 3 instead. This will move control of the central heating function (which is actually hot water now) to the hot water function, so in theory this should resolve the problem.

It begs the question though why is it like it is? Is it wiring incompetence, or is there a reason why it has been done. Has the HW channel of the programmer failed? If it doesn't work, it will require further investigation. Don't worry about trying the above you in effect are just picking up a live supply for the black wire from another switch, to the one that it does now, so it won't cause any damage.

Edit
Having just re read your first post, I noticed your upstairs thermostat is not programmable. Does this mean that this zone is also being presently controlled by the central heating settings of the programmer? (ie to the same on / off times as the HW is presently) if so, the above change as well as moving the hot water, will also move the upstairs heating zone to being controlled by the hot water channel, as there is only one wire presently fitted to terminal 3 which will be feeding them both. If this is the case some rewiring of the programmer and thermostats will be required.

I suspect that it's likely that the system was originally designed as a single zone heating system and when the building regs stipulated new homes must have more zones that it was modified by someone who didn't quite have a full understanding of the wiring.

 

[JunglieD]

Thank you both for your responses.

Old & Bold - yes, I do need the programmable stat for downstairs. This MEP2c does not currently have any influence over heating whatsoever. Just the Hot Water timing alas from the ‘Heating’ side. The last owner did just live with it and I may need a pro in to properly diagnose if Stem’s suggestion doesn’t work.

Stem - thanks for the re-wiring advice. I will try that this evening. Regarding your edit and the comment about the upstairs stat, it is functionally independent of the MEP2c and is not set or influenced by the configuration on it at all ie. both ‘sides’ of the MEP2c can be off and the upstairs stat will still initiate heating when the temp is adjusted above ambient (and the downstairs programmable one). This, in fact is a follow up query I will have if I get the MEP2c Hot Water ‘side’ sorted - how to get the upstairs zone set by a timer to avoid the rather digital approach of just setting a temp and letting the heating kick in and out all day/night. I suspect the easiest option would be to replace the fixed stat with a programmable one but maybe it could be linked to the MEP2c if the ‘Heating’ side becomes available....

 

[stem]

Thanks for the explanation. What you say adds to my suspicion about it being made into a two zone at the last minute (or tried to be made into one)

If I read your last post correctly, the upstairs heating is available 24/7 regardless of any programmer 'on' times. If so that is crazy. The purpose of the building regs introducing the multiple zone control was to improve energy efficiency, not make it worse!

If my suggested modification works, then the now available terminal 4 which is for the Central Heating 'on' signal could be utilised to give control of the upstairs heating on/off times. Now it maybe that if the upstairs zone is available 24/7 then it could be fed via one of the brown wires connected to the Live terminal, if so, simply moving it from there to terminal 4 will provide the control you require. You would have determine where the live supply to the upstairs thermostat comes from to be sure though, it could be connected to the downstairs programmable thermostat supply instead.

Let's see what happens tonight.

Having said all of that, as the property is only 6 years old, I think you have good reason to get in touch with the builder and inform him that the system was not wired up correctly when it was built.

 

[JunglieD]

Thanks Stem - I'll try that and report back later. You did read that right - the upstairs heating is available 24/7 regardless of programmer on times (it is crazy so I am in a constant battle with my wife over the stat setting!). The upstairs MRT1 has the following connections:

BROWN > 1
BLACK & GREY > 3

Like you say, let's see what happens tonight and tackle this 'upstairs' issue later - I'll follow up with the builder next week if this escalates - Redrow were the developer so I guess they bring in contractors and we're well outside of snagging now so it would be a judgment of whether they'd consider this under NHBC...

 

[JunglieD]

Stem - your re-wiring advice for the MEP2c has worked a treat. Removing the brown wire linking L and 3 then moving Black from 4 to 3 means my Hot Water is now operating from the 'Hot Water' side of the box and my OCD can relax a little! Thank you so much! The heating zones appear to be unaffected by this change - downstairs still functioning correctly by the MPRT programmable stat and the upstairs remains operational in the un-timed fixed stat configuration it was before....

For cherry on top, do you think there is a way of linking the upstairs fixed stat to the MEP2c now the 'Heating' side is free/available? Wiring to the upstairs MRT1 is as pictured:

Thank you again for your assistance. I'm really grateful.

ETA - that is Brown > 1 and Black & Grey > 3

 

[stem]

Excellent news! glad it worked.

OK so we will have a go with upstairs stat now. The upstairs thermostat must be being fed from somewhere, we need to find out where.

Having removed the link previously, there will now just be two live wires in the L terminal at the MEP2c. One of them may supply just the upstairs thermostat. and one will be the live supply to the MEP2c.

As a test, can you safely remove them, one at a time, so that the other remains connected. There will be a live supply coming in on at least one of them, so take care to insulate each wire when it is removed, and see what happens.

When the wire that is the live supply is removed then nothing will work.

If you find that with one of the wires removed, everything works, except the upstairs heating. Put the removed wire in the now vacant MEP2c terminal 4. If this doesn't happen, report back what occurred. It's quite possible that none of the heating works when the wire is removed, but even if that happens it is useful information for the next step.

 

[JunglieD]

Stem - thanks for your continued assistance, I got back later than expected today but tried your suggestion and have some more information for you. Before I begin, the photo below shows the current configuration of the MEP2c now Hot Water is controlled correctly by the 'Hot Water' side:

Because your recent advice had me trying the different combinations of 'Live' wire I'm pointing (with a pen) to the left hand wire that I'm calling 'L1' in my results below. I'm referring to the Right hand one as 'L2'...

1) First Up - With L1 removed (and L2 remaining in position) there is no power at all to the MEP2c.

2) With only L1 in position (and L2 removed) there is power to the MEP2c but the boiler will not fire up from any of the following i) upstairs stat ii) downstairs stat or iii) demand for Hot Water to the 'On' position from the MEP2c.

Because configuration 2 did not give me the desired outcome, I did not try moving L2 to the now vacant Terminal 4 - thought it was best to report back to you first!

 

[stem]

Yes you did right. Put both lives back where they were for now. That was pretty much what I expected.

When the wire that is the live supply is removed then nothing will work.

It's quite possible that none of the heating works when the wire is removed.

In the case of the second, whilst I thought you may loose both upstairs and downstairs heating, I expected the hot water side should still be working. Likely it was just that the hot water cylinder thermostat was already full of hot water, so wasn't calling for heat at the time, so didn't fire the boiler. It would be worth checking though just to be sure.

So, it looks like both thermostats. upstairs and downstairs are connected to the same live, based on that I have two suggestions for you.

1) If the hot water does still works as per the above, then replace the downstairs programmable stat with a standard stat like the one upstairs (ie not a programmable stat) and move the wire to terminal 4. Then the central heating settings on the MEP2c will control the times for both upstairs and downstairs heating together.

This goes a bit against the principle of having separate time control for upstairs and downstairs which has the idea of having separate zones, so that downstairs is heated during the day and the bedrooms only in the morning and at bedtime to save energy. However, doing this is still much better than the heating being on upstairs 24/7 as it is now.

2) If you are prepared to, and able to run a new wire from the upstairs thermostat to the MEP2c vacant terminal 4 then just the upstairs can be driven from the MEP2c and the downstairs can stay as it is with the programmable thermostat.

Let me know what you think.

 

[JunglieD]

Hi Stem - of the two suggestions, I prefer Option 2. I'm not attracted to Option 1 at all because I like having zones even if the hard on-off is a frustration. Can I suggest a 3rd Option though where I replace the upstairs stat with a programmable stat - would this be a practical solution albeit wasteful of the 'Heating' side to the MEP2c?

Also - I am minded to try my test configuration 2 again (where L2 is removed) because I want to be sure that the hot water thermostat assumption you made is accurate. After I re-connected L1 and L2 I did put the Hot Water to 'On' and the boiler did fire.... I suppose it's conceivable that the hot water tank/thermostat gave a different signal but it was only about 2-minutes after my attempt in test configuration 2...

 

[Johnmdc]

@stem Presumably the brown that was disconnected was the live feed to the grey on the 2 port valves, so by disconnecting that the boiler wouldn't get a feed when the valve opened.

@JunglieD Is there another brown wire not connected behind the programmer? You appear to have a wire missing.
As there are 2 blue wires there should be 2 corresponding brown wires (twin and earth wires) then there are the black and grey wires there should also be a corresponding brown wire (3 core and Earth) so 3 brown wires in total.
Can you post a picture of the inside of the joint box where your valves and pump connect. (Probably near your hot water tank)

 

[stem]

Option 3 is a good solution and would work well.

The Heating Side of the MEP2c would remain unused of course (not good for the OCD though. Believe me I know!)

If you did get a programmable thermostat for upstairs, it would need to be a battery powered variant (I believe that Myson MPRT you downstairs is battery powered, but not all are) Because you only have two wires, you won't have a neutral present that a mains version requires.