Advice requested on Installation issue

JohnPerriam

Our central heating system comprised:-

             Worcester Bosch boiler Greenstar Danesmoor Utility fitted about 9 years ago.

             Drayton LP522 Timer / Controller (wired)

             Drayton thermostat for down stairs (wired)

             Horstmann DRT 2 thermostat for upstairs (an integrated thermostat and a timer) wired

The system has been piped with three motorised 2 port valves to control water heating, downstairs central heating and upstairs central heating.

When the system was first installed we took some time to understand how best to control the upstairs heating and found that the only way to get the upstairs heating to function was if the downstairs heating was programmed to be on (but not necessarily demanding heat). We thus would turn the downstairs thermostat to minimum (10C) at night and ensure that both upstairs and downstairs timers had overlapping ON times for the morning and this worked well.  In effect we learned that this was not a full two zone system as it relied on the downstairs heating being on before upstairs would turn on.

I assumed that we could use the same logic (wiring) as noted above but replace the Drayton LP522 controller and Drayton thermostat with a Tado Wireless Smart thermostat Stater kit V3 + (from Amazon). The installation went very well.

At first, we were pleased with how well the system functioned. However, after setting the timers for hot water and central heating to match the previous system we found that the upstairs heating did not come on.

On investigation, what we found was that the upstairs heating would only come on when the downstairs heating was on and supplying heat. The old system worked when the downstairs heating was on but not necessarily supplying heat. If we stay with the new Tado system we will be heating both upstairs and downstairs at the same time thus costing us more.

After thinking about the situation I now believe that we need a full two zone central heating system.

Can someone offer any advice please?

GrilledCheese2

I think I know what is happening here. Can you take a photo of the wiring for the Wireless Receiver and post it in a comment. I'm particularly interested in what is wired to CH NO.

wateroakley

Like grilled cheese, I too would be suspicious of the wiring logic.

JohnPerriam

Hi There,

Many thanks for the replies.

I post a picture of the wiring of the wireless control box as requested.

Thanks for taking the time to help.

Regards

John

GrilledCheese2

I was hoping to see two wires connected to CH NO, but I can only see the one. In the attached drawing is my assumption of how the heating is wired (prior to installing Tado). Thermostats, programmers and motorised valves are basically switches and all the switches in a row need to close for the boiler to switch on. Your Drayton programmer was switching on the power to both the up and down thermostats. You now need to modify the wiring so that the upstairs thermostat is permanently powered. In the drawing the wire highlighted in yellow needs to move and be connected where I have drawn the red dotted line (permanent live). We've established the wire is not connected in the programmer/receiver, so it is likely to be connected in the wiring centre. The wiring centre is usually a white rectangular box with lots of wires going to it. If you're comfortable with electrics you could remove the cover from the wiring centre and post a few photos from slightly different angles. Might be possible to identify the highlighted wire. Otherwise you'll need an electrician to update the wiring.

JohnPerriam

Hi Grilled Cheese2,

Thanks for the reply.

The Upstairs thermostat (Horstmann DRT2) is a battery powered unit and has no mains power to the unit.

I am happy to remove the cover on the wiring centre and take a picture of the wiring. I have to take the Grandkids out and so will not be able to send the pictures until this afternoon.

Again Thanks for the advice.

John

GrilledCheese2

Whilst the thermostat is battery powered it will need a Live wire connected. The DRT2 is switching the Live on and off, which provides the 230V for the motorised valve to operate.

JohnPerriam

Thanks GrilledCheese2,

The previous system worked with the DRT2 thermostat wiring it is just since we changed to the Tado system that the upstairs heating will only work once the downstairs CH is on and the boiler is firing. Prior to the change the downstairs CH just had to be on but not necessarily heating down stairs.

I have had some advice from Tado and they are saying that I need either to have a separate Tado thermostat and use that to fire the boiler independently of the programmer or keep the DRT2 and rewire so that it is an independent system. It may well be that your advice is spot on and in addition we need a separate circuit to the boiler / 2 port valve.

Thanks for taking the time to help us, I will look to see what is involved in separating the upstairs circuit.

Regards

John

GrilledCheese2

The Drayton programmer was providing the time control, which gave power to the two thermostats that then provided temperature control. When you installed the Tado system I guess there was an instruction to connect two wires together when you removed the old Drayton thermostat. This is due to the new receiver now providing both time and temperature control in a single switch. It's this single switch which is now preventing you from having two thermostats working independently. I've edited my drawing to show the wiring now that Tado is installed and the old thermostat removed. Hopefully it makes it clear why the highlighted wire needs to be moved.

JohnPerriam

Hi Grilled Cheese2,

Thanks for the advice. It makes a lot of sense, I had not realised that the Drayton controller supplied power to both thermostats.

I was thinking that we had a wiring issue where the live to the Horstmann thermostat was connected to the downstairs zone valve and thus we only got power when the downstairs valve was operating.

So I opened up the wiring centre and found the most awful bird nest of wire and individual choc blocks. Shocking!

I then closed the lid thinking I may have to put the old controller and thermostat back.

As proof of your concept could I remove the current live from the Horsmann thermostat and then run a separate wire from the supply to the wiring centre directly to the Horsmann thermostat it is a long run but on a temporary basis it would prove your idea.

Very well thought out. Thank you again.

Regards

John

GrilledCheese2

Yes, as a proof of concept you could run a separate Live to the thermostat to prove my theory is correct.

Alternatively, if you're brave enough to open the wiring centre again, you could try the following. The wiring centres are always a mess inside and you do have to be careful not to knock any wires out of place.

1. Identify the motorised valve for the upstairs radiators.
2. Follow the multi-core cable from the valve and identify the brown wire.
3. The brown wire is a Live input - It activates the motor inside the valve
4. The brown wire will be connected to another wire in the wiring centre.
5. This wire will go to the Horstmann thermostat. Identify the second wire in the same cable.
6. This second wire needs to move to permanent live.
7. The grey wires from the motorised valves will usually be connected to permanent live. Identify where the grey wires are connected and move the thermostat wire to the same screw terminal.

Before making any changes take a note/photograph of the wiring so that you can return the wire to the original position if my advice is incorrect.

JohnPerriam

Hi GrilledCheese2,

Well done, you are absolutely correct.

I did not have the bottle to get into the wiring centre so ran a separate live wire from the wireless centre live to the common terminal of the Horstmann after removing and capping the original live from the Horstmann common terminal.

I then turned on the upstairs CH and the boiler fired up (no light on the wireless controller as it is not controlling the upstairs heating).

I checked out the downstairs heating and it also fired up.

I can now control both up and down stairs independently.

The next job is to get into the wiring centre and make the changes permanent. I have some questions but if OK with you I will ask them later.

Once I have the wiring properly sorted I will buy a Tado wired thermostat to control upstairs heating.

Thanks again I would not have been able to sort this out without your advice.

Regards John