We have a solution to this problem by moving the stat arm. Note current production (Jan 23) has a perforated stat arm which does not have this issue. (NVXSTD04601AH)
Duo LX heaters with nuisance overheat tripping.
Where we are having nuisance tripping on the secondary overheat stats of LX Duo’s, we have identified an effective onsite solution which requires moving the capillary phial to the outlet of the unit. This still retains the safety feature if the main fan on that side were to ever fail.
The capillary phial is currently located half way across the rear side of he duo’s and positioned between tubes 2 and 3 from the top of the heat exchanger
Method
Remove the louvre frame from the outlet opposing the burner for easier access.
Remove the 4 screws from the phial cover plate and remove plate.
Remove the two screws holding the phial bracket in place and retain screws for later.
Remove the 4 screws from the high limit stat box and pull out being careful not to damage the wiring.
Move the loose phial bracket and repositioned to the back of the stat box.
Using the two screws from earlier, carefully screw the capillary phial bracket to the rear of the stat box ensuring the phial is towards the fan side (see photo opposite and above) and being careful not to damage either the IMIT stat or cable or copper Phial within the stat box.
Screw the stat box back into position (see photo below)
Screw the loose plate back to the unused aperture.
From the inside of the unit, carefully coil up the loose copper phial back close to the stat box ensuring it does not fall towards the heat exchanger tube.
Refit the louvre frame.
Run the heater to confirm the operation of the stat.
Location of capillary phial on the outlet of the heater
once repositioned.
