Megaflo 28 system boiler

[darkart]

Have a problem with a Megaflo 28 System boiler: Error 20 appears on the digital display.

Fan comes on, nothing else happens, the boiler shuts down showing 'error 20' Fault code

After several attempts, the Error 20 code will not clear, even when I turn off the power to the boiler and turn the knob to reset for 5 seconds?

I referred to instructions and checked the following:
Flue: Clear no blockage
Flow switch: seems ok
Condensate: Clean

Could it be the NTC Sensor?
How do I test it to make sure that's at fault before I buy a new part?

 

[hertsboilers]

As far as I remember, Baxi error code is in this format: E1 followed by 33, so we call E133.

What about yours?

 

[darkart]

As far as I remember, Baxi error code is in this format: E1 followed by 33, so we call E133.

What about yours?

Error table quote says go to section E, which says its a temperature sensor fault.
What I cant understand is why cant I clear the error code when using the 'reset' control knob to see if the boiler goes to the same fault; it just stays on the same fault code constant?

 

[hertsboilers]

Checked again, E20 - Central Heating NTC Fault.

It it is NTC fault, it need to be replaced.

 

[Agile]

Can he do that without compromising the room sealing of the boiler?

 

[bernardgreen]

It it is NTC fault, it need to be replaced.

The resistance of the NTC thermistor is measured by a circuit on the PCB, that circuit could be mal functioning.

It would be worth comparing the resistance of the existing thermistor against the data in the specification for the device. Or if that data is not available then against the value of the replacement thermistor.

 

[hertsboilers]

The resistance of the NTC thermistor is measured by a circuit on the PCB, that circuit could be mal functioning.

It would be worth comparing the resistance of the existing thermistor against the data in the specification for the device. Or if that data is not available then against the value of the replacement thermistor.

You just don’t understand our practice work!

In such a case, it is more likely by a failed NTC not by the board, ie, NTC being open circuit or short circuit.

 

[bernardgreen]

You just don’t understand our practice work!

I dealt with enough sensors on production equipment, both service and design. though to be fair most were PT100 due to the accuracy required.

 

[hertsboilers]

I dealt with enough sensors on production equipment, both service and design. though to be fair most were PT100 due to the accuracy required.

I feel you always pick up bone from egg?

E20 error code, in theory it can be the sensor, can be the connectors, can be the loom, can be the board, even can be over heat, no circulation..., do we need an endless list?

 

[Agile]

I feel you always pick up bone from egg?

Direct translation from the Chinese! 鸡蛋里挑骨头

 

[bernardgreen]

in theory it can be the sensor, can be the connectors, can be the loom, can be the board, even can be over heat, no circulation..., do we need an endless list?

No just a logical way to decide which of those is the fault. Does the fault finding flow diagram for this boiler provide data for resistance checks or does it concentrate on part exchange ?

NTC being open circuit or short circuit.

or being out of spec, being the wrong resistance for the temperature, and thus the control is getting a false temperatuire reading.

 

[Agile]

or being out of spec, being the wrong resistance for the temperature, and thus the control is getting a false temperatuire reading.

That virtually NEVER occurs.

I have only ever encountered one!

That was because water had entered the inside where the element is.

 

[darkart]

Thank you all again for your kind help, you all have mentioned numerous causes so will have a play about tomorrow to determine what the fault is, enjoying the puzzle to be honest, will let you know when I solve it.

 

[slippyr4]

Other than testing whether the NTC is open circuit or not, trying to test its resistance is a mugs game. You need to know it's beta value, and it's current temperature, and then do some maths, to work out if it's reading right or not.

Add to that the fact that these things don't tend to fail other than catastrophically, and that a new part is only a fiver or so, and you see once again why a sensible, professional plumber would just change it and see if the fault goes away, but a google warier would advocate waste far more money in terms of a plumbers time pratting about with a circuit board.

 

[bernardgreen]

trying to test its resistance is a mugs game.

Should be no need to calculate, and besides it isn't always a linear temp / resistance function.

Testing is simple, an ohm meter and a thermometer.

Then use the manufacturers data... This is for the Vishay/BC Components NTCAIMME NTC Miniature Immersion Sensor so do NOT use it for the sensor in your boiler.

As to not verifying the resistance is appropriate for the temperature. If you ( and your customer ) are happy with a boiler whose temperature control is not accurate then so be it.