Do you have SW3-1 turned on that is required to allow the input from the 2nd thermostat.

mine is wired as 2 zones and if I had my time again I would wire it as 1 zone running off a single thermostat as a max temp cut off.  If you have 2 zones that work independently the HP is more likely to cycle on and off due to low water volume to heat leading to poor efficiency and increased wear

Thanks, Gary, - I've tried it with SW3-1 turned on - but still get the L5 error.  I assumed that SW3-1 was purely to change the operation depending upon the thermostat contacts being normally open or normally closed.

There is also a statement in the installation manual that says "When Dip SW 4-1 is OFF, 2-zone temperature control and 2-zone valve ON/OFF control is not available."  So I've changed SW4-1 as well, although in the table of DIP Switches it states that SW4-1 is for multiple outdoor units.   I've also tried changing SW4-2 to set to Master - but in each case I get the L5 error.

Posted by: @gary

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mine is wired as 2 zones and if I had my time again I would wire it as 1 zone running off a single thermostat

I take your point about a single zone -it has been running as a single zone but I'd like to try with more control.  Also it has now become a challenge to achieve it!

@bryanb

You may find the following video of use.

Derek's video link makes a good point, what have you got the zones set up as in the FTC controller, if you are using the main FTC controller to measure room temperature to control the rads that should be set as main RC and if you are using a third party thermostat as the controller for the UFH for zone 2 that confusingly should also be set as main RC, if its set as anything else it will be looking for a signal from a Mitsubishi wireless controller that you don't have, that could create the error you are seeing.

Thank you Derek and Gary.  I'm using the wireless thermostat to control the temp for the rads and a third party one to control the UFH. So from the video it looks as if Zone 1 should be set to Room RC and Zone 2 to Main RC.  I'll try that later. Thanks.

Posted by: @bryanb

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Thank you Derek and Gary.  I'm using the wireless thermostat to control the temp for the rads and a third party one to control the UFH. So from the video it looks as if Zone 1 should be set to Room RC and Zone 2 to Main RC.  I'll try that later. Thanks.

The main point that I was making was the need to switch the controller off and then back on for DIP Switch changes to take effect.

I had been doing that - the whole system was shut down between changes.  But I hadn't made any changes to the main controller but it looks as if I can't do that without changing the DIP switches again to enable a second zone.  

Still no joy!  With SW2-6 and SW2-7 turned on I can see two zones and set Zone 1 sensor to be Room RC1 and Zone 2 to be mainRC (instead of TH1).  However I am still getting the L5 error to do with the indoor FTC thermistor.

I've also tried with SW4-1 and SW4-2 turned on - as in the manual it states these need to be on for 2 zone control - but it doesn't affect the L5 error.

Mine may be older and different but on mine SW2-6 is for a mixing tank and the manual states that SW2-7 only works if SW2-6 is off.

SW4-1 and SW4-2 on mine relate to using multiple outdoor units as master and slave and don't relate to multiple zones so these are also off.

Posted by: @bryanb

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Still no joy!  With SW2-6 and SW2-7 turned on I can see two zones and set Zone 1 sensor to be Room RC1 and Zone 2 to be mainRC (instead of TH1).  However I am still getting the L5 error to do with the indoor FTC thermistor.

I've also tried with SW4-1 and SW4-2 turned on - as in the manual it states these need to be on for 2 zone control - but it doesn't affect the L5 error.

I suspect that you are getting an L5 error because under 'Room Sensor Settings' you are trying to allocate RC1 or MainRC to zone 2, whereas the device installed is actually a thermostat (On/Off device) rather than a temperature sensor (Thermistor). I suggest that you set Zone 1 to TH1 or MainRC and leave Zone 2 unselected.