Replacing OJ Electronics MTU2 Underfloor Heating Sensors

[bobzy20]

Hi,

Does anyone know what could replace these old OJ Electronics MTU2 underfloor heating sensors? Apparently these are discontinued by OJ Electronics, so was looking to replace with something more modern.

Also, does anyone know how to remove this from the wall?

 

[Roddy Young]

Hello,
We have OJ thermostats and controls. They simply pull out and off their backplate - but they are quite stiff.

Here is a link to OJ:

MTU2

Recommended for control of underfloor heating and electrical heating.

ojelectronics.com

Googling suggests they may still be available in Europe.

 

[bobzy20]

Hi Roddy,

Thanks for your reply.

When you say 'we', do you mean 'you' or are you referring to OJ Electronics?

Reply from OJ Electronics.
If your floor heating system is water based, we regret to inform you that our WLM/WLTM hydronic product lines (and with also the hydronic MTU2) have been discontinued.

OJ stopped producing all hydronic floor heating controls in 2019, along with the closure of the UK subsidiary.

We don’t have the expertise in house, for this product and we do not have anyone in the UK anymore.

Consequently, we do not have a replacement product and cannot provide further assistance.

 

[Roddy Young]

I mean we have OJ controls in our house. Sorry about my ambiguity.

Your reply from OJ does suggest it will be difficult to find replacements.

 

[bobzy20]

Hi Roddy,

Thanks for the reply. Sorry, reading it again makes total sense!

So, to remove the thermostat, I just need to pull the part that sticks out and it will unclip? I still need to find a replacement, but until I remove it I cant see how it is wired.

Thanks

 

[Roddy Young]

Our thermostats were made by OJ about 2010 and branded Rehau.
They are a different style to yours but I suspect OJ use the same sort of mounting arrangement.
The middle part simply pulls outwards - it's held in by friction. There is no latch to release or screw, etc.
Of course I can't guarantee yours are the same.....
Roddy

 

[bobzy20]

Thanks Roddy,

Is your system hydronic (water based) or electric?

Do you also have a master panel somewhere that these sensors link to?

Thanks

 

[Roddy Young]

Ours is water based ufh with a manifold with 10 circuits.
The actuators on the manifold are wired to an OJ control box - circled in the photo.
Roddy

 

[bobzy20]

Thanks Roddy.

I don't have any of that, so it must be electric under-floor heating.

In this case perhaps finding a replacement thermostat won't be so hard.

 

[bobzy20]

Looks like I might have found a replacement thermostat - Heatmiser neoStat-e V2.

This is for electric underfloor heating.

I will confirm if all working once its installed for clarity and content for this post for future reference.

 

[bobzy20]

Could someone on here help with the wiring as per the attached document. Have I got the wiring to match correctly from the old thermostat top (MTU) to the new one at the bottom.

Also, does the polarity matter on the heating wire and floor sensor?

Thanks

 

[stem]

The diagram you posted shows the correct connections. The numbers in red on the neoState-e correspond to the MTU terminal numbers.

So:

1=Live
2/3=Neutral
4=Live Load
6/7 Floor Sensor

The heating element and floor sensor [ETF='ElectroThermal Feedback' which is generated from a resistor that provides a temperature dependant resistance value] are purely resistive, so normally no polarity, but if you keep them as they are (i.e. in the same terminal numbers) it won't be an issue if they're not.