Hi Gary, haven’t seen full numbers on your error code but UD appears to be an overheat protection code. 

You could also do an Info request… like the flow rate enquiry. or, in this case, an error history enquiry. 

Enq code 103 is last error

Enq code 104 is second to last error

Enq code 105 is third to last error 

I don’t know how these enquiries would be displayed.

but hope this helps

Thanks it doesn’t provide anymore info just says UD-0

@gary I’ll ask Mitsubishi for some insights, and hopefully they can provide some clarification. Have you called their support line?

@editor thanks Mars just waiting for support to open at 8am

@gary after a quick document scan the UD0-0 error suggests a communication error between the outdoor and indoor units, or sometimes between components like the controller and the main PCB. Will be interesting to see if that’s correct and what Mitsubishi have to say.

Agreed that a Google search offers nothing, with this thread being the first search result 😂

@editor I found some info in the service manual it could be a bad condensing temperature or pressure sensor.

It shuts down the heat pump if condensing temperature is over 70C.

Does anyone know what typical condensing temperatures should be?

@gary my Mitsubishi contact recommended you call the support line, and sent me this.

As far as I know (and I stand to be corrected) in normal operation, typical condensing temperatures on an ASHP are usually in the 40–60C range, depending on flow temps, load and outdoor conditions. Hitting 70C is high and usually a sign of something going wrong like a faulty sensor, blocked heat exchanger, poor flow or even a stuck valve. 

@editor thanks Mars that’s the same table I found in the service manual it’s does feel like it’s the sensor that’s at fault.  When it stopped it was reading 74C.

I managed to get the heat pump running this morning  at 32C flow temp but the condenser temp was reading 65C so if you are correct this also points to a faulty sensor.

The heat pump has now been off for 3 hours and it’s reading 68C which doesn’t seem likely.

£400 later and it’s fixed it was the T3 sensor that measures the condensed refrigerant temp it should read single figures was reading 65C and occasionally above 70C which is when it trips the error.

Gary, might I enquire how old the Ecodan unit is? I am just trying to get a measure on the economics of the Mitsubishi service package, which includes all parts, and the random failure costs. £400 for a fairly minor sensor helps focus the mind!