Ariston Microgenus 31 - DHW Flow Sensor problems

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Hi all, just after a little advice on a DHW flow sensor problem I'm having.

I've noticed recently that the kitchen hot tap needs to be turned to approx half of full flow before the boiler ignites and heats the water. I'm certain it used to turn on at a lower flow rate. Additionally, we recently replaced the shower head with a snazzy one that has micro-jets and which uses less water. The shower now keeps going cold which I can see is because it is using less water, the hot flow rate gets below the threshold and the boiler turns off.

This all points me to the flow rate sensor. I have tried the easy fix and changed the electrical switch as it simply clips onto the HDW inlet by the secondary heat exchanger. However, this hasn't improved the situation at all.

So I now turn to the mechanical part of the sensor - I gather from the internet that this is a part that commonly fails on the Microgenus range. I have ordered and have received a replacement part (this one).

I was going to replace it this weekend as it looked like a simple job. I thought I could turn off the hot/cold water and drain the DHW part of the system, leaving the boiler heating and heat exchanger loop untouched (other than being switched off). The top of the cartridge looks like it would fit an 18mm socket so I thought it would be simple to unscrew and replace with the new one. Unfortunately it appears to be slightly smaller than 18mm but too big for 17mm as the 18mm socket slips as I apply pressure therefore I'll therefore have to remove it with a spanner. The limited room means I'll have to remove the pump and auto air vent so will have to remove the side panel and also therefore remove the cupboard which is boxing in the boiler - this makes it a somewhat larger job!

I just wanted to check therefore that replacing this part is indeed likely to improve the sensitivity of the flow rate sensor?

Thanks in advance - couple of pics below...


 
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I use an 18mm ring spanner on them, is your socket maybe worn ? when you run the hw does the little neon on the sensor flash or flicker or is it solid red.
If you are in a hard water area they can be a real mare to get out
 
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Thanks for the reply Ian. I have an 18mm ring spanner but it's fractionally too big and slips round the head of the cartridge. My old socket set jumped from 17mm to 19mm so I bought a new one to get an 18mm and that feels a little tighter but still slips. I wondered if the head was an imperial size but none of the imperial sockets fit it.

Regarding the led, it is either solid red when above the flow threshold or completely off when below the flow threshold. There is no point at which it blinks or flashes. I do notice when turning the tap up gradually that as soon as the led comes on, the water from the tap immediately starts to pulse slightly. It stops pulsing when flow is reduced such that the boiler cuts out. Not sure if that is significant? I'm fairly sure it didn't used to do that.

Thanks
 
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Google universal socket otherwise an imperial socket should fit. WD40 it and let it soak in.
 
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Regarding the led, it is either solid red when above the flow threshold or completely off when below the flow threshold.
normally when the turbine is faulty the LED flickers or flashes, so it might be something else , but as you have bought one anyway just change it
 

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