Ariston Eurocombi help please - Fixed

In that case there should be no issues with finding out why the boiler does not work. Operation is sequencial. You have a halt in this sequence. Get the multimeter out and with aid of boiler manual it will be easy to locate the defect.
 
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There is obviously a fault!

But I am surprised that you are using hot water for so long and so regularly.

There are several possibilities as to why the boiler is stopping. Knowing what makes it come back on would be a clue!

Obviously correctly diagnosing the cause is the first step in repairing!

Tony
Tony are you gas safe mate
 
Blooflame. what makes you think our Tony is not Gas Safe registered?

He is Argi registered (see his signature)
 
Blooflame. what makes you think our Tony is not Gas Safe registered?

He is Argi registered (see his signature)
Well, I read the forum mate, just seems everything is gained via here oh and the name is a clue. Anyway it's a legitimate question ain't it?
 
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Blooflame, better watch it or Tony will be having words with you.
 
In that case there should be no issues with finding out why the boiler does not work. Operation is sequencial. You have a halt in this sequence. Get the multimeter out and with aid of boiler manual it will be easy to locate the defect.

I've followed the fault checking from the manual and looked up answers here (and googled) and that has led me to post up this thread.

I understand that there is something wrong with the sequence of events that fire and shutdown the boiler but I'm at a loss as to what component would prevent the burner shutdown sequence.

I've looked for sticky relays and failed sensors. I was hoping (maybe naively) that someone may have had experience of this failure and could point me in the right direction.

Tony has been helpful, and if it is as he suspects something to do with the anti-cycle circuit then I'll finish off tracing the circuit and attempt to fix.
 
I can only produce a suspect based on evidence!

The test with a fixed resistor in place of the sensor would have created a static power setting and you would have then seen if the actual fault then presents.

The only way to fix faults is to diagnose them first. Diagnosis is achieved by carrying out tests!

Tony
 
I will do the two tests that you proposed (hair dryer on the ignition box and replace boiler temperature thermistor with fixed resistance).
Thanks again for looking and replying.
 
Ran tests as per //www.diynot.com/forums/plumbing/ariston-eurocombi-help-please.294076/#2145612

Cool hairdryer on ignition box doesn't measurably alter the burner shutdown sequence or allow reignition.

Replaced boiler thermistor with 2.3kOhms resistor and the boiler temperature keeps rising without shutting off (hit 90C so I stopped)
The boiler temperature LEDs stayed at a constant 70C (as I would expect with a static resistor value)
In my logic this rules out the thermistor being faulty, does it tell us anything else?

The burner shut off is still controllable using the CH potentiometer.
The fan still keeps running after burner shutdown.
 
2.3 K is about a third of the 6.8 K that I had suggested.

It was not any old resistor but one which would keep the boiler on at near max power.

2.3 K should have modulated the boiler back to relatively low power.

You should have been doing that on hot water demand. The whole idea was to see if the fault presents whilst the boiler has an apparent stable demand condition.

So far you have not tested what I was hoping for.

By the way, has anyone been fiddling with the boiler settings?

Tony
 
Replaced CH thermistor with 5.8K (this shows as ~40C on the temp LEDs)
The burner seems to be operating at maximum output whether the demand is DHW or CH.

The only way to get it to modulate is to turn the CH temp knob to min.

The boiler now continues to heat without shutting down I stopped testing when my temperature probe reached 90C

By the way, has anyone been fiddling with the boiler settings?
No one has fiddled with any settings on the boiler (I presume you mean the other screwdriver adjustable potentiometers)
The only setting that is ever adjusted is the CH temp

I have noticed that the solenoids that operate the gas valves are really quite hot, 50C. Is that normal?
(EDIT: solenoids seem to soak up the same heat as other metal parts in that area)
 
It does sound as if the gas valve is either faulty or it is seriously misadjusted.

They normally would only get gently warm.

I would say that you need a competent gas registered engineer.

Particularly one who can check the adjustments before replacing it although replacement is quite likely to be needed.

When a new gas valve is fitted it still needs to be set up to provide the right settings for the boiler. This is one of the reasons an enginneer is needed.

Tony
 

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