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Andrew Smith
Andrew Smith, Plumber
Category: Plumbing
Satisfied Customers: 3629
Experience:  City and Guilds qualified plumber
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Hi, I have an Ariston Microgenus 24 HE MFFI combination boiler.

Customer Question

Hi, I have an Ariston Microgenus 24 HE MFFI combination boiler. It is set to 'Economy' mode and the central heating works fine; however, there is no hot water from the shower. When I change the boiler to 'Comfort' mode, the hot water works. 'Comfort' mode keeps the water in the secondary exchanger hot and apparently is not the normal state of operation. What could be causing 'Economy' mode to fail?
Submitted: 3 years ago.
Category: Plumbing
Expert:  Andrew Smith replied 3 years ago.
You are quite right, the comfort mode gives you a hot water preheat. Can you turn the heating off and leave the boiler for 2 minutes, then run the hot tap and tell me if the boiler fires?
Customer: replied 3 years ago.

Hi Andrew,


thanks for your reply. When you say "turn the heating off", do you mean turn the entire boiler off, wait 2 minutes, then turn it back on? Or something else?

Expert:  Andrew Smith replied 3 years ago.
Yes, turn everything off
Customer: replied 3 years ago.
Tried that, unfortunately no change!
Expert:  Andrew Smith replied 3 years ago.
Does the boiler fire at all with the heating off and the tap running?
Customer: replied 3 years ago.
When set to Economy mode it doesnt, no.
Expert:  Andrew Smith replied 3 years ago.
Does the boiler click when you run the hot tap (you may need to put your ear against the side)?
Customer: replied 3 years ago.

Apologies for the late reply. Yes, the boiler does click. What does this mean?

Expert:  Andrew Smith replied 3 years ago.
Clicks but does not fire up?
This is pointing to an electrical fault on the divertor valve.
Are you able to take the cover off and see it in action?
Customer: replied 3 years ago.

What exactly am I looking for?

Expert:  Andrew Smith replied 3 years ago.
On the right hand side there will be a big brass valve with a piston that should push out when the tap is run?
Customer: replied 3 years ago.

I can't easily access the inside of the boiler - is there any other way of identifying whether the diverter valve is in order?

Expert:  Andrew Smith replied 3 years ago.
When on economy mode. the divertor valve fires the boiler.
It is hard to say what the problem is without being able to get inside the case.
Perhaps it is time for an engineer.