An Arizona 5 Master & Slave HRV system (the control panel with up and down black arrow key) was installed at my own property at July 2010 and it has been working fine. Recently I checked the filters lifespan remained, after quickly pressed the FUNC key twice (when press this key one more time get 3% filter lifespan remained), the ROOF TEMP location has no display and the ROOM TEMP location has display (digit 9 a couple of days ago, and it changed to 10 from yesterday), but before there are displays at both the ROOF TEMP and ROOM TEMP locations. Is there a fault in the system now?

I opened the control panel to check the electronic circuit board to see whether there is any problem and it looks fine, just a little bit dust and some "spider silk" like stuff on the circuit board, and I cleaned it away with some electronic circuit board cleaner, then installed the control panel back to its previous status, but the control panel display problem is still the same.

The whole HRV system is still working fine (the ventilation level is in the range of 1 to 6, and it has been set to 3 at this winter season), the temperatures displays (for roof, room and set temperatures) on the control panel is fine, the fan can speed up and slow down during the day, if turn off the power from the control panel, the fan can stop running. There is no condensation on the windows at the early morning, and the environment inside the property is dry, the air is f othresh and clean. The roof cavity should be dry and clean, and the roof insulation material was renewed at about 4 years ago and the new roof insulation material can last for 50 years.

When quickly press the FUNC key twice, what do the displays on the ROOF TEMP and ROOM TEMP locations represent? what are the range of values of these two display? Are these two displays adjustable and how? At the moment, for the HRV control panel in my place, only the ROOM TEMP location has display when quickly press the FUNC key twice. If this is a fault, is it on the control panel, roof cavity master control unit, sensor or the communication link between the master control unit and the control panel? Is this a problem needed to be addressed quickly, otherwise more serious problem will be occurred later on?

I contacted with the installer for this display problem, but none of them are helpful.