Baxi Duo Tec/Potterton Promax Combi HE/Main Combi HE.
The serial numbers on these boilers all begin with 3 letters, followed by some numbers. The first 2 numbers are the build year, the second 2 the build week. The rest are random. So for example, a 28 HE A Duo Tec built in the 23 week of 2010 will be CAC1023XXXXXXX.
E119 - Low water pressure - Look for water leak coming from the water pressure switch of the diverter valve spindle. Also check and re-charge the vessel if required.
E133 - Failure to ignite - On older models built pre 2010, the ignition electrodes warp with the heat. They are now re-designed and much better. As a temporary fix, bent them back to make the gap the thickness of a pound coin.
E131 - (not listed) - Can be caused by a few things, sometimes if 2 fault codes come up together, such as E133 (failure to light) then E119 (low system pressure). It can also be caused by power failure during fault code.
E168 - Communication Error (not listed) - Most likely the PCB. Check the voltage and polarity before ordering a replacement.
E160 - Fan fault - Most of the time the fan is faulty. Check the loom to it. If you unplug the rectangular connector block, the fan should run at fall speed. If it doesn't, the fan is definitely goosed.
E20 - CH NTC sensor fault - Most likely needs replacing.
E50 - DHW NTC sensor fault - Most likely needs replacing. Could have been caused by a leak from the it's gasket. It can then corrode the sensor and the loom. This fault should still provide CH, just not DHW.
E110, E125 and E193 - Circulation fault - Pump could be seized or faulty. Also worth checking is the filter located in the return isolation valve behind the blanking cap or (if fitted) the integral filling loop.
Another fault that I have come across a couple of times is with boilers fitted with a verticle flue. The boiler doesn't provide enough hot water. When it fires up, the boiler becomes noisy and eventually goes out. Check the air intake side on the flue test point. If the CO rises the plastic flue exhaust could well be cracked. You'll have to pull the flue apart to check it.
The gas valve on these boilers also need adjusting, the CO2% should be 8.7 on high and 8.4 on low. Adjustment is made on the gas valve, the throttle for high is behind the blue cap, the offset on low is behind the brass flat headed cap.
To ACCESS SERVICE MODE - Turn the potentiometers to min, then turn the DHW potentiometer to the 3 o'clock position and back to the 12 o'clock position twice. The display should change briefly to SF, the LEDs flash and the boiler should light up. Turn the CH potentiometer to MAX (will display 00) for max fan speed and turn back down to MIN for minimum (will display 0). The temp should then cycle with the letter P. To get out of service mode, turn the DHW potentiometer to any position from 12 o'clock (min).
