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sirweste

Morco F-11E cutting out

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Hello all,

 

Hoping someone can shed some light on the fault with my Morco hot water heater. 

It’s an on demand jobbie, so lights when there’s water flow. But then after a few seconds it shuts the gas off and lights up its red light on the display. 

 

Ive tried bending the (that I think is a) thermocouple down towards the flame but it’s had no effect. Also no effect from changing the flame setting knob or water temp. 

 

So im stumped as what to do next. Order the thermocouple unit or the water flow sensor. I’m assuming thermocouple. 

 

Any advice would be appreciated!

 

 

 

Cheers!!

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Deleted because I should have watched the video prior to posting. 

Edited by WotEver

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Is it actually a thermocouple? No I think the flame supervision is by means of flame rectification - checking for the ionising (and hence conductive) presence of flame, and measuring the rectification effect due to the large burner “ground” and the pointed electrode sensor.

 

Anyway presuming that the sensor electrode is actually bathed in flame when it is lit, and there is nothing shorting the sensor to earth, it is probably the control electronics.

 

Unlikely to be the flow sensor as it is detecting flow to light the boiler in the first place. If the flow sensor decided there wasn’t enough water, it would just shut the flame off not light the fault light as well.

Edited by nicknorman

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2 minutes ago, nicknorman said:

Is it actually a thermocouple?

Silly me never bothered watching the video. You’re right, that’s not a thermocouple. 

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8 hours ago, Mike the Boilerman said:

I'd say that was an overheat error but it happens rather too quickly I suspect. 

 

What does the manual say is the meaning of that red light that comes on as the flames extinguish?

 

It only mentions coming on due to failure to ignite/burn. Having read it, it also says the electrode module should be replaced every 3 years so that might be a clue.

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Cheers for the replies.

 

Just read the electrode replacement every three years, it's been installed for ~ 5 now I think.

 

Though I had concluded that it was likely to be the flow switch or electronics board given the spares that are sold on ebay i.e. unusually, given the three year replacement, no one is selling the electrode assy.

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Got one working a few years ago, the problem was spiders below the terminal  on the top of the boiler not letting the air / exhaust mixture be correct. If you take off the top of the terminal it is the first bit of gubbins you see, a bicycle pump sorted it out.

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@J R ALSOP I'd just read this, there's more spiders in my house than stars in the galaxy I think.

Might drive home at dinner and have a go at this. Could be the one. Cheers

 

 

image.png.1b3674879a734b59d3f9f9312f098e93.png

 

 

Edited by sirweste

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1 hour ago, nicknorman said:

It only mentions coming on due to failure to ignite/burn. Having read it, it also says the electrode module should be replaced every 3 years so that might be a clue.

 

Well given the video shows smooth and solid combustion when the red light comes ON and the gas is turned OFF, I'd say this is actually flame detection failure. 

 

I've never encountered until now a boiler that needs electrodes replacing as periodic maintenance, but given the manual demands it, I'd say do it. Then when it still doesn't work, replace the PCB. Check condition of the leads, connections etc first though.

 

I note the PCB notices the flame presence and stops the spark, but also turns off the gas and the red light ON ten seconds after ignition. A suspiciously round figure often used as a threshold period for flame detection.

 

 

 

2 minutes ago, sirweste said:

there's more spiders in my house than stars in the galaxy I think.

 

House? Is this installed in a house? Is it running on Natural Gas? Doesn't look like it to me!

 

 

 

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Yer the cut off time is exactly the same each time. Which doesn't lend itself to a variable like a blockage does it.

 

I wondered if it was something to do with heat, but with temp and flame turned right down the symptoms are the same.

 

Sorry, by house I mean I'm a liveaboard, it's the first dwelling I've ever owned so I think of it as a house!

 

Found the board and electrode assy for next day delivery if ordered before 1:45. So early dinner to check for spiders and connection condition. Then I'll get both items ordered and if it's cured with the electrode I'll return the board.

 

cheers

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59 minutes ago, Mike the Boilerman said:

 

I note the PCB notices the flame presence and stops the spark,...

 

Surely the spark will intrinsically stop if the electrode is bathed in flame? The flame is ionised gas which is highly conductive. And the spark is also ionised gas. In other words, it is impossible to have an electrical-type spark within a flame.

Edited by nicknorman

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Interesting bit of science that. The middle "probe" is called a confirmation electrode, so I think there is a flow between the left (lookers) and centre electrode....?

 

 

image.png

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25 minutes ago, sirweste said:

Interesting bit of science that. The middle "probe" is called a confirmation electrode, so I think there is a flow between the left (lookers) and centre electrode....?

 

 

image.png

Interesting. Three electrodes is surely unusual?

I can’t quite tell from the video but it looks like the spark is between the spark electrode and the confirmation electrode, as opposed to between the spark electrode and the burner which I would have thought would be more normal. I suppose this allows the control electronics to tell that the spark is definitely in the right place, not in the wrong place due to dodgy wiring and insulation.

 

Normally the flame conduction detection is between a pointy electrode and the large mass of the burner, which results in differential conduction between alternate half-cycles of the ac waveform and hence the control electronics can differentiate between conduction by a genuine flame vs a soggy bit of grass or a spider bridging the gap.

 

Edit: just reminding myself (by looking it up!) that the differential conduction -Or flame rectification as it’s known - occurs because the tip of the electrode is glowing red hot whilst the gas burner at the base of the flame remains relatively cool. Just like a heated cathode in an old glass TV valve.

 

So reliable flame failure detection can’t work between two electrodes both bathed in the top of the flame.

Edited by nicknorman

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2 minutes ago, nicknorman said:

I can’t quite tell from the video but it looks like the spark is between the spark electrode and the confirmation electrode,

 

Yes spark is between 10 (right) and 9 (centre)

 

The Ionisation electrode is angled over horizontally towards the Confirmation electrode.  Suggesting conduction between the two.

I dont recall any of them being "pointy"

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1 minute ago, sirweste said:

 

Yes spark is between 10 (right) and 9 (centre)

 

The Ionisation electrode is angled over horizontally towards the Confirmation electrode.  Suggesting conduction between the two.

I dont recall any of them being "pointy"

See my edit to previous post. I refreshed my memory and it isn’t to do with being pointy, it’s to do with relative temperatures.

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1 hour ago, nicknorman said:

See my edit to previous post. I refreshed my memory and it isn’t to do with being pointy, it’s to do with relative temperatures.

 

Old twin electrode rectification did rely on the differing surface areas but these were, i understand, prone to false positive results if debris was present so the changed to a different type of FD not relying on rectification, which doesnt do this and which i don't understand yet. It usually uses a separate electrode from the sparker for detection, hence the three electodes on this boiler. 

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Sounds correct. From an earlier SN there was only 2 Electrodes according to the parts list. One's on order direct from Morco, hopefully will arrive tomorrow, I ain't a man enough to enjoy cold showers.

 

On the spiders front, I couldn't get the flue puzzle to pieces in the 15 minutes I had at home

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I guess it couldn’t hurt to give both the left and centre electrodes a gentle rub with some fine emery paper. Whatever the mechanism it still relies on making a circuit. 

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6 minutes ago, WotEver said:

I guess it couldn’t hurt to give both the left and centre electrodes a gentle rub with some fine emery paper. Whatever the mechanism it still relies on making a circuit. 

The internets said not to do this when I read them. Apparently

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2 hours ago, sirweste said:

The internets said not to do this when I read them. Apparently

Oh, ok. I guess they’re plated then. 

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1 minute ago, Tony Brooks said:

Or they worry some ham fisted bod will bend them.

Indeed. If it was mine I know what I’d do :)

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On ‎18‎/‎09‎/‎2019 at 10:58, sirweste said:

 

Found the board and electrode assy for next day delivery if ordered before 1:45. So early dinner to check for spiders and connection condition. Then I'll get both items ordered and if it's cured with the electrode I'll return the board.

 

cheers

Many suppliers will not accept the return of PCB's .

Flame rectification on gas burners relied on a milliamp current earthing through the carbon content of the flame. With heat, the rectification probes become resistive. Any spiders or dust on the probes would be there before the flame, and consequently would give a false flame signal to the controller thus preventing ignition.

Edited by Ex Brummie

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