Wiring up a thermostat (RF-Switch Heatmiser) to Ideal Mexico

[Bodger&Badger]

Hi Everyone,

Long time lurker, first time poster.

I'm trying to upgrade the heating controls for my mother's boiler, it's probably 30 years old and needs upgrading itself but that is a later task.

At the moment I'm upgrading it from a timed hot water and heating, to thermostatically controlled heating. To confirm this IS A GRAVITY HOT WATER system and pumped central heating.

The part I am totally confused about is how to wire the thermostat (reciever) up. I have included wiring diagrams from both the boiler manual as well as the manual for the reciever and finally what I have been able to confidently wire up so far. I also have purchased 25m of 5core central heating flex so I have 5 colours to choose when wiring, (Blue, Brown, Yellow/Green, Black, Grey) - I know this won't match the diagrams but just to bear in mind if i need to double it up for more cores.

I have two pumps that need to be wired in paralel to the A terminal block (2A and 6A???, can you confirm this is correct?) I can follow a wire diagram but i'm not sure what it is, I just can't get my head around these two and how to wire them up.

To try and simplify things I have added letters to the other terminals, so for instance connection needs to be made from 3 > 1A > 3B.

Thanks in advance
B&B

 

[stem]

Fully pumped systems were being installed in the early 1980's so it's likely to be older than 30 years. The problem with a Gravity Hot Water / Pumped Central Heating is that it is not possible for the CH to operate independently from the HW.

So:
HW = Boiler 'on'
CH = Boiler and Pump both 'on' [However, as the boiler is 'on' the HW will also be heated by gravity circulation]

Unfortunately I'm not too sure of the way the Heatmiser works internally to be 100% sure of how it would take to your type of system. If the boiler was connected to the Heatmiser 'boiler' terminals [LS (Live Supply) would go to a permanent live and LR (Live Return) would go to the boilers L terminal] and if the Heatmiser 'boiler' switch operates when either CH or HW were 'on' then that's fine. [However, the diagram you posted shows the HW controlling the boiler via a microswitch inside the HW motorised valve instead of Heatmiser boiler LS & LR which may mean the boiler doesn't work via the boiler switch in HW mode ]

The pumps would connect to CH NO1, so they run when the CH was 'on' [this assumes that both pumps are installed so that they operate together and not independently]

If my assumptions are correct, then:

1. With HW only 'on' the Boiler Switch starts the boiler and hot water circulates by gravity circulation through the hot water cylinder.

2. With CH only 'on' the Boiler Switch starts the boiler and the CH NO1 starts both pumps

However, if the boiler switch inside the Heatmiser doesn't operate when the HW is on, then the above won't work and a more complicated installation would be required. So my first port of call would be to wire it up on a bench and find out when the Heatmiser 'boiler' switch operates. However, if you're lucky, someone my read this thread and know the answer.

 

[Bodger&Badger]

Hi Stem,

Thank you so much for your reply.

You are totally right, I was trying to be kind to the boiler, it was made in 91 so definitely over 30 years old.

I've also been in touch with Heatmiser and they have been helpful as well. They've given the go ahead for this wiring diagram and if you can't see anything wrong with it, I'll do a bench test.

Thanks for that suggestion by the way, I’m the kind of person who would forget to do something so simple that saves a lot of frustration.

Even better it looks like I’m going to be able to use just one run of 5 core cabling which is excellent.

The thermostat I’ve bought thankfully also can have a hot water schedule as well so I can’t wait to get rid of the old system and have some thermostatically controlled heating for a change.

Thanks again Stem.

B&B