My Th132 AF has started to dim the display once the thermostat kicks in and turns the heating on, then comes back to normal once the heating goes off? any ideas please??

Try a Power Reset. Disconnect all mains power to it for 15 minutes, press and hold any button for 1 minute. Reconnect the power. If that doesn't fix it, the thermostat has failed and you need a new one. Most have backup batteries that can cause the issue you are seeing, but the manual doesn't mention anything about batteries in the base unit.

Aube Technologies TH132 A/F/AF Owner's Manual

ManualsLib https://www.manualslib.com > ... > Thermostat

View and Download Aube Technologies TH132 A/F/AF owner's manual online. Aube Technologies Control Module Owner's Guide. TH132 A/F/AF thermostat pdf manual ...

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possible power supply if voltage to display bad board

replace the thermistat module..sounds like it has a bug in the firmware

You can reset the programming of the comfort setting and make sure that it did not get set at 14C. Here is the manual that shows how to do that.
http://www.aubetech.com/manuel/2/TH132-A-F-AF-230.pdf

This product has 2-year warranty against defects in workmanship.
Aube technologies Inc.
Warranty does not apply to poorly installed ...
Canada 450-358-4600

Manual does not have troubleshoot section.
section 4 includes temperature setpoints by model number.
On-line manual can be word-searched for fine details that might be missed by a visual read.
http://waterheatertimer.org/pdf/TH132-A-F-AF-230-thermostat.pdf

Check that air vents are open to control, so the unit can read correct temperature.
Change temperature Display selector for F or C.
Make sure wires are connected to correct terminals to match your voltage.
15 amp max rating indicates #12 gauge wire for 120Volts. Recommend that thermostat control a contactor instead of direct-wire to heat coils.
Example contactors
http://waterheatertimer.org/H230A.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Well, if it wasn't doing that before then you more than likely know its in your wiring. Cools down then heats back up sounds like the auto change over is on, and the heat setting is higher than the cool setting?

http://www.uheat.co.uk/aube_th132_underfloor_heating_thermostat.htm

TH132 is a thermostat for under-floor heating
Go to the website above and download on-line copy of your manual
On-line manual let you read bigger print & lets you break down the steps easier

I am sure by the time this answer reaches you, the problem will be solved
This is true because manuals are frustrating, until you tell somebody it can't be figured out >> which gives you time to rest >> after which the manual makes sense.

BUT I am frequently wrong, and you may be at a standstill
A quick look at the manual.
You can also select which part of the manual is giving you a problem and then I will help you through that specific difficulty

Wiring: I guess the instructions at bottom of manual apply to your model
Your 240Volt hot wires from breaker box connect to terminals 1 & 5
Your two wires supplying power to heat connect to 2 & 4
Pilot wire to terminal 3
Floor sensor to 6 or 7 >> wire from sensor can connect to either pole
The TH132 has two sensors, 1 located inside the TH132, the other sensor located in floor

Set up:
The first part describes 10 buttons (right away you know this is complicated)
There is a brief description of both sensors
Step 1 shows how to configure the start and temp-display switches

Step 2 covers installation of module on base
I guess you hook up power at this point because the display is supposed to light up
This implies that the bottom part of manual should be located more towards the top, and the power-up directive seems to be missing. Bad manual.
Step 2 shows what the display looks like with first power-up

Step 3 tells how to set current time and day.

Step 4 adjust temp setpoints >> floor temp is pre-programmed to 82 degrees

Step 4 shows that you press-and-hold the sunshine or moon button to have it display
The sunshine button is the upper temp setting, the moon is the lower temp setting

Step 5 is operating mode > choose automatic for programming to operate

Step 6 is programming, which carries on with about 24 steps
If this is your problem area, let me know
Now the manual suggests you make a chart of your programs
Other programmable devices don't work when there is a conflict in programming

Wow I see the TH132 is 'equipped with a proportional adaptive controller..' that carries a two year warranty. I'm sure you'll rest easy knowing that.

Reply back with the specific trouble area, and we'll get it going for you.

the thermostat sends a signal to the circuit board. Not knowing anymore than I do about your heater or furnace I would suggest that that is a good place to start. Any limit or safety switch wouldnt coincidentally shut off the heater when it reached the set temp.

I have also had the same problem with 2 units. I have been in touch with Aube who say they have identfied a problem with the back unit which they will have fixed in " a few months time". My suggestion would be to contact them for a replacement later on this year