Myson Midas SFI Assistance req'd

[Trance Nation]

Afternoon all.

Boiler is : Myson Midas SFI GC no. 47-494-04

Intermittent fault on HW, CH appears to work as per normal. Fault occurs approx 1 in 3 times. Here is my description of what i noted when the fault occured and some previous work done on the appliance. The initial fault was crappy ignition occasionally not sparking which a new ignition PCB cured today. Of course as the boiler now ignites, i have discovered this further fault.

When calling for HW, boiler goes "through the motions" and fires up on a low fan & flame. It does NOT go to high speed fan therefore as a result doesnt go to a high flame. Out of interest i loosened the combustion cover front panel and low and behold it went to high fan & flame. When the cover was tightened again it did NOT drop back to low. I have came to the conclusion that perhaps the fan is running slow on a low speed and not producing enough air for the airflow sensor to signal the board to go high. Does that make enough sense or just coincedence ?! Lights on PCB are 2,3,5,6. 2 goes out if fan makes high speed. 5 appears to be HW demand, 3 fan demand (?), 6 i have no idea. Theres no diagram/explanation of the diagnosis of what the lights mean.

I exchanged the airflow sensor today (brand new unused one from van stock) incase that was the prob - guess what it wasnt !

Ignition PCB also replaced today, this was the original fault as mentioned above.

There are no obstructions to the flue - air inlet is clear (its rear exit i can see straight out it) and a torch up the inner flue from outside shows no probs either.

CW, HW and CH sensors were replaced by me approx 6 - 8 weeks ago due to CH never satisfying. The tenant mentioned that the HW seemed to "act up" early last week and the boiler eventually packed in (with ignition prob) on saturday. I assume there was 2 or more faults on this appliance.

Any asistance greatly appreciated. Perhaps it is a "slow" fan on low, or is the main PCB not understanding the signal from the airflow sensor ?

Cheers for reading, soz re: long post !

 

[corgiman]

Cor I aint seen one of these for donkeys years!!!!

and I cant remember much about them sorry, if you get no replies from anyone else it maybe worth getting someone professional in

sorry

 

[ollski]

Is that the ancient midas with the 2 blue pumps and the airflow sensor in a metal case on the top....if it is I had exactly the same a couple of years ago and it was sorted with a new air flow sensor.

 

[baxpoti]

Extract from http://www.partsarena.com/baxi/

To assist fault finding six light emitting diodes (LEDs) have been incorporated on the main control board to indicate certain functions

of the board. By using these LEDs it should be possible to identify where the problem lies and to rectify.

LED 1 -Will remain on until the fan has produced enough air for complete combustion allow rate — low rate air detector.

LED 2 - Will remain on until the fan has produced enough air for complete combustion at high rate — high rate air detector.

LED 3 - On when there is a demand for the Ian at high speed.

LED 4 - On when there is a demand for the central heating pump.

LED 5 - On when there is a demand for the hot water pump.

LED 6 - On when the main board calls upon the full sequence control board to light the main burner and turn on the fan (speed selection depends on LED 3).

 

[Trance Nation]

Thanks for the led explanation which i have printed off for future refernece and to the "senior technician" at Potterton for his assistance on the phone.

Problem was cured today with a new airflow sensor, yes i was right the first time by replacing it on my initial visit to the property on monday - turns out the one i replaced it with was faulty which didnt help matters at all ! A quick swap today and its solved.

Anyhooo jobs a good 'un now. Damn sharp edges on those boilers, jeez !