Ariston micro Genus 27MFFI

[Archie3cat]

Problem on DHW. The boiler works perfectly on heating but when hot water is called for the the flow is good (normal) the temperature rises (on the indicator lights) to 70, the water is nice and hot. After a few seconds the flame cuts out, the pump keeps running and the flame reignites after, say, 20 seconds when the temperature is lowered.
This may happen once, rarely twice then the situation remains in balance with a good continuous flow of hot water for as long as you want.
I have looked at a previous problem on the forum and it mentions a clip type temp. sensor on the lefthand boiler pipe but the sensor on mine is fixed on the top elbow as it enters the chamber.
About a year ago this forum was a great help on another problem of which the advice I took was to fit a new secondary heat exchanger. I also fitted a Magnaclean unit as well.
Everything worked perfectly until about a month ago when I drained down to change a radiator. I have vented all the radiators many times and also the vent above the pump. The DHW temp control is set on max.
Your kind advices will be greatly appreciated, regards...Ivan.

 

[crashndie]

from the problem your discribing is the hot water gos hot then cold then hot?

this could b the domestic hot water thermistor stat reading faulty does the boiler make a singing noise like a kettle boiling?

 

[parky]

I had one of these boilers (and had every possible thing go wrong with it)

The temp sensor in the primary circuit is apparently prone to failure. When mine failed it went intermittent for a long time. This caused the temp display to jump from the "real" temp 60-70 degrees and zero. This also had the effect of making the boiler gas valve to oscillate from full on to half on (sounded like a Geiger counter it did it so quickly). I analyzed it by putting a multimeter on the thermister (on the left hand side primary pipe near the elbow as you describe (roughly above the diverter valve) and when I wiggled it with the meter attached I could see the resistance reading going to infinity - so it was intermittently failing .

However I would expect to see that on both HW and CH.

I didn't think there was a thermister in the secondary circuit, the boiler only measured the primary circuit - again hence it being strange your CH is fine.

What do the temp LEDS show when the boiler cuts out? as they are directly reading that thermister, if they also go off, it at least points you in the right direction. You say the pump keeps running, but does the fan?

 

[Archie3cat]

Many thanks for your prompt replies. I have done a couple of tests this morning and ...guess what..it is behaving perfectlly now! (I suppose it's like going to the doctor).
It is going up to the 70 light and staying there with a very good hot water flow. On one occasion it did drop to 60 but regained to 70 after abot 10 seconds.
There is a temperature probe in the DHW circuit positioned in the brass casting of the diverter valve unit. there has been no sign of 'kettling' and I think that the fan keeps running. When the gas cuts out the indicator lights step back to 20 but of course step back up again to 70 when the flame is restored.
As a general observation I do not like the 'push on' plastic thermister connectors, they seem a bit flimsy and due to age could be brittle.
Thanks for your kind attentions...Ivan.

 

[parky]

apologies, you are right, the DHW probe (which is also used to control the CH water temp) is on the diverter valve. The one further up the pipe is the overheat sensor.

When mine went intermittent the lights were jumping from 70 to 20 instantaneously, and back again) which was causing the boiler to oscillate, rather than them actually reflecting the temp of the water. If yours are staying on and dropping slowely (in line with the steadily cooling water when your boiler cuts out) then I doubt it is the sensor

The only other similar problem I had was when my air sensor was dirty. It was more apparent when the boiler was hot (due to the warm air being thinner mayber?) The boiler would cut out but the fan would stay on waiting for the air sensor to say there was enough flow, and it normally started up again (as the air cooled a bit) , but over time got worse (as it got more full of dust I guess)

Easy to fix as it is held in by two screws on the flu pipe and then simply blowing through it can clear it enough - however it is annoyingly contained within the combustion chamber so there is the RGi issue.

 

[parky]

Here is the link to my original problem and how it was solved

//www.diynot.com/forums/viewtopic.php?t=15251