Vokera Mynute 14-48 SE Elec issue?

[aidanb]

Hope someone can help with this old relic of a boiler!
Basically it won't fire up, gone through the flowchart and there is no 240 to the gas valve.
As it mentions to check voltage between terminals 3 and 4 on the board, it was not there, both terminals had 240v to L though (as if both terminals were N). Assumed this was the fault, so swapped the board for a new one, same problem again.
This leaves me with 2 neutrals at the gas valve, rather than a live and neutral.
All stats have power passing through, the fan and pump are running..

Any ideas?

Best add, i'm an electrician hoping its a basic electrical fault, anything other than that will be left to someone else

 

[Doodlebug]

How do you know the fan is running? Can you see the fan?


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[aidanb]

Actually i'm just assuming because of the noise and vibration, the pump seems near enough silent. To see the fan while it is running would mean taking the inner cover off, which i'm not keen to do!
According to the chart, the fan running will cause the differential switch to energise terminal A, which is energised. (the chart does say this after a short period will energise the gas valve, but it never does)

Am i along the right lines there?

 

[Doodlebug]

Is there an overheat switch or low pressure switch on this boiler? Without booting up my laptop I can't see what your looking at. Have you got wiring instructions for the boiler. Have a look at the sequence of operation in the instructions. If pump and fan are running it could be air pressure switch hasn't made, overheat operated, low pressure switch operated, sensor fault, I'm assuming there is no power to gas valve and no spark.


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[Doodlebug]

Oh and glad you said you haven't removed the case. ;-)


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[aidanb]

It has main thermostat, safety thermostat and high limit stat in series, all of which are passing 240v through
There is the boiler flow switch which powers the fan (along with a fan overrun stat), though this is ~115v and apparently this is correct voltage in the book.
Then there is the pressure differential switch, has 2 tubes to the flue area, and that passes 240v

There is no power to the gas valve, and I cannot see a spark

 

[aidanb]

Just found this simplified version on another site,

Mynute SE 14/48, 20/70, 28/96 with Ineco/HubaSequence of Operation
Start
Link out 1 and 3 on terminal strip to by-pass any external controls.
Power out on 1 and back on 3.
Pump runs.
240v through P1-1 on main stat.(white wire)
240v through safety stat. (yellow dot. White wire.)
240v through hi-limit stat to 1 on ignition box.
118v out on C (blue/black)
118v back on B (red/black)
240v out on E (red/white)
Flow switch makes and 240v to fan.
Fan runs.
PD switch makes, 118v in on A (brown)
Boiler sparks and lights.
Fan overruns at over 80c via fan overrun stat and n/closed and common of flowswitch.


I have everything up to 'boiler sparks and lights'. Brand new ignition box and same apparent issue!

 

[Doodlebug]

14/48, 20/70 AND 28/96 SE MYNUTE WITH INECO AND HUBA

START.

Link out 1 and 3 on terminal strip to by-pass any external controls.
Power out on 1 and back on 3.
Pump runs.
240v through p1 -1 on main stat. (white wire)
240v through safety stat. (yellow dot white wire)
240v through hi-limit stat to 1 on ignition box.
118v out on C (blue/black)
118v back on B (red/black)
240v out on E (red/white)
Flow switch makes and 240v to fan.
Fan runs.
PD switch makes, 118v in on A (brown)
Boiler sparks and lights.
Fan overruns at over 80c via fan-overrun stat and n/closed and common of
Flow switch.


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[Doodlebug]

There's another sequence with Brahma box, which have you got?


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[Doodlebug]

Are you getting 118vin on A (brown)?


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[Doodlebug]

I'm wondering if the air pressure switch has even made.


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[Doodlebug]

I've got a sequence I can go through with you, step by step if you'd like?


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[aidanb]

It is the Ineco box on this, and yes I have around 115v on A, B and C, and 240v on E and 1.

I took one tube off the differential switch, blew through it and it switched, and i'm sure I can hear it switch when the power is turned on/fan comes on? That 118/115v on A should confirm that, is that right?

I can't guarantee there isn't a spark though, I don't think its ever been visible like the blue flame is when its running

 

[Doodlebug]

Step by step check.....

Is 240v Ac present at terminal 3 of terminal block?
Does pump run?
Is 240v Ac present at both terminals of safety thermostat?
Is 240v Ac present at both terminals of hi-limit stat?

If yes to all of above

Is there 240v Ac present at terminal 1 on ignition control box
Is fan running?
If yes wait of delay,
Spark at electrode?



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[Doodlebug]

It is the Ineco box on this, and yes I have around 115v on A, B and C, and 240v on E and 1.

I took one tube off the differential switch, blew through it and it switched, and i'm sure I can hear it switch when the power is turned on/fan comes on? That 118/115v on A should confirm that, is that right?

I can't guarantee there isn't a spark though, I don't think its ever been visible like the blue flame is when its running

If you have 118v at A then yes that should confirm that the switch has made.


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[Doodlebug]

Is there approx 115v Ac present at terminal A on ignition control board?
Is there approx 115v Ac present at terminal B on ignition control box?



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[aidanb]

Yes to both, seem to have voltage everywhere it is supposed to be apart from terminal 4 for the gas valve!

Any idea what voltage the electrode would be at? I had 10v or so earlier

 

[Doodlebug]

If all the above checks are ok, the manual says to check wiring and connections to pressure differential switch.

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[Doodlebug]

Yes to both, seem to have voltage everywhere it is supposed to be apart from terminal 4 for the gas valve!

Any idea what voltage the electrode would be at? I had 10v or so earlier

Can you get a spark from the board where the electrode lead connects to?


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[Doodlebug]

You say you changed the board, I think there is two variations of board on this boiler.


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