Ariston combi hot water problem

[steve1000]

Hi

I have a ariston microgenus 23 combination boiler, the problem i have is with the hot water only, central heating seems fine. When i run any of the hot taps fully open the boiler delivers hot water for about 30 to 40 secs, the the burner cuts out for about 10secs causing the water to go cold. It then kicks in again for 40secs supplying hot water and carries on going on and off for these time scales. If i open the taps less so the water is slower the hot water stays hot no problem without the boiler cutting out at all.

Any Ideas would be helpful, not sure of age of boiler but moved in 2 years ago and it was already in premises.

look foreword to your replys, many thanks

steve

 

[Agile]

Sounds like a blocked plate heat exchanger.

Tony

 

[AMEdinburgh]

We had the circumstance, you describe with one of our Worcester 350s.

Replacing the heat exchanger (as suggested by Agile for you) solved the problem.

 

[steve1000]

Thanks for your responses

Would that be the main heat exchanger or the secondary one.

cheers steve

 

[AMEdinburgh]

Hello Steve,

You would be best waiting for agile if he's on line later as he's the professional and has a comprehensive knowledge.

If your boiler is like my Worcester, the heat exchanger for the water is a rectangular metallic object about the size of a man's hand and about 30mm thick plus the outlet pipes. On mine, it was not within the sealed combustion chamber where the the main exchanger for the heating is and where the flames are!

I was lucky enough to find a surplus new one for mine on Ebay at a real bargain (£36 inc postage) and it took me about 45 mins to fit. Was a bit of a fiddle though. In the past I've bought from mjtcontrols.co.uk who have given me a good service at prices much better than available to me as a punter from local merchants. If you're looking on their site, best search using the Appliance GC number which will be on the instruction manual or hopefully on the boiler somewhere. That will take you straight to the list of parts.

 

[Agile]

The plate HE is the secondary one!

Tony

 

[steve1000]

Thank you both for all your advice and quick responses. Will go and change that and hopefully solve my probs.

Thanks again

steve

 

[steve1000]

Hi i eventually got secondary heat exchanger out today to have a look before i purchased a new one and found it very clean, on flushing it out.. the reason i got round to it today is that the boiler is still doing above fault, but has also developed a new one. What it also does now is that when hot water tap turned on, the pump kicks in on boiler but the burner does not fire causing me to get cold water. if i tap front of boiler just above control panel burner then kicks in then keeps going as long as tap not on too fast. very strange. any help appreciated before i purchase secondary heat exchanger.
cheers
steve

 

[steve1000]

Just an update:
had british gas out today as burner stopped kicking at all last night on both hot water and central heating no matter what i did. they replaced pressure switch which got it working and he checked taps all ok. when i got home from work tried hot tap on full and original problem still happens but later fault all now solved. am now on there homecare and they are coming back friday to fix broken flue outside, so will tell him then. thanks steve

 

[steve1000]

british gas came back today and fixed flue. he said that hot water going hot and cold when tap on fast is normal for a combi boiler, as the heat cannot pass from primary circuit to water for dhw aswell when flow rate high, so primary circuit temperature max's out causing boiler to shut down for a few seconds until this drops. is this correct or do i need second opinion. look forward to your replies
cheers steve

 

[mickyg]

he's talking nonsense.

 

[Gasguru]

....he said that hot water going hot and cold when tap on fast is normal for a combi boiler

Complete garbage from BG as usual. The higher the flowrate the more likely the burner will stay on max.

If the secondary heat exchanger really is clean then get them to check the differential pressure across the air pressure sensor. Ariston screwed up the flue restrictors. Once these boilers age, air pressure sensing becomes marginal and the standard flue restrictor requires removal.

Otherwise it could be a temperature sensor fault.

What London postcode are you?

 

[steve1000]

i am actually tw13 Feltham by heathrow airport.
thanks for advice

 

[steve1000]

when i had secondary heat exchanger out and rinsed out, no sludge or muck came out. i could not see inside very well so suppose could be limescale!!

 

[steve1000]

assuming temperature sensors ok as when i turn dhw dial nown i see flames reduce. and also when i adjust central heating dial down when central heating on the boiler cuts out and comes back on when dial turned up.
thanks again steve