Ariston MicroGenus 27mffi

[sav]

Got the above boiler with a hot water issue, it's runs for about 5 mins ok then turns off runs cold then fires up again. Does ths over and over


any ideas? Could it be dirafram in diverter valve nackard as the flow / return pipe gets hot as well or could it be the diverter valve nackard?

cheers

 

[mfgs]

is the diverter motor moving? Think these have the black motor on top of the valve, take it off and call for hot water and then heating and see if its moving up and down to change between the two. Have had a few of these that have been knackered.

 

[lame plumber]

more likely an nct/thermistor losing its resistance check and replace

 

[SafeGasInstall]

I had one where the water flow was about 20L/min all I did is turn it down to 12L and problem solved !

 

[bewsh]

does it still do it if the combustion case is open slightly? If so, you're probably looking at an air pressure issue - Have a look at the fan, give it a clean, remove the flue restrictor, etc..

 

[Dsgas]

Check rectification probe as when flame modulates down it can lose signal. NTC and high limit ( loses calibration) also worth checking which have been said already. These worked for me. Diverter defo worth checking if your losing heat to the primary circuit.

 

[breakdown]

Blockage in plate heat ex ?

 

[sav]

Changed the diverter valve moter and it sorted it for a few days now back to the same.

Should I try the hot water thermistor next?

Dont work on these much as you can prob tell.

thanks for the info guys

 

[stevetheplumber]

i would clean the hex

 

[Deleted member 32524]

Are you running it on HW only? If it is on HW & CH I am sure the divertor opens to clear heat away from boiler? Run it on HW only and see if flow gets hot. Then switch it and if it opens then you know it is ok and that was why it was getting hot. As said check resistance through sensors, if they are good it could be the dhw plate. What is the water like, black? Might need a flush. Was the motor a wet pocket? cos you might have temporarily unblocked it when you drained down. Sounds like the thermistor is doing its job though, as it is not going to lock out on the overheat, but still could be on the way out. Give flame sensor a good clean with wire wool.
TBH it could be any one or more of any of the stuff that has already been suggested by others. Good luck.