Ariston EuroCombi A/23 or A/27 Heating comes on by iteself

[TonyWallingtonSM6]

I've had an Ariston EuroCombi A/27 combination boiler for over 10 years and for the past 4 months it has developed a fault - the Gas Central Heating would come on by iteself for approx 20 to 30 minutes & then turn itself off for a few hours before turning itself back on again etc... a constant cycle. This would happen throughout the day & night regardless if we turned the boiler just to hot water only.

Looking throughout the internet, one of the initial solutions was to change the Microswitch for 3-way/main flow group (its a £12.28 part 5733340) however this did not resolve the problem. Everywhere I looked there were different opinions on how to resolve so....

After speaking to a engineer who has worked on these boilers for over 20 years, he advised the above would not have resolved the problem as the central heating was coming on by itself regardless if anyone used hot water or not. The solution to the problem was either ;

A) The temperture probe for the central heating system needed replacing

e.g. if this was not working, the boiler would enter "Frost mode" , regardless if CH was turned on or not, so it would automatically come on every few hours to prevent the cold from freezing up pipes etc.... (original Part number 569236 but since replaced by part number 998458 £3.87 http://www.deansgas.co.uk/ariston-temperature-probe-998458-microcombi-23--27-10666-p.asp)

Or it would be

B) Faulty program clock


As the temperture probe was only £3.87, we tried A) & YES IT WORKED STRAIGHT AWAY ! & has continuned to work over the last 7 days

The reason I'm making this post is to help others who have the same problem with their bolier. This is a very reliable boiler so don' scrap it if you can fix this easily.

The www address for the part is shown under A) above & it really is very simple to replace (took 10 minutes in all)

 

[Theydonites]

Hi Tony,

Thank you for posting the info about the temperature probe. My in laws boiler is having the exact same problem as you described. I've fitted a new temperature probe but sadly it doesn't appear to have resolved the problem. The temperature probe that I took out was quite dirty, can you remember if yours was the same?

I'm now wondering if replacing the diaphragm would help? The pin comes out of the 3 way valve when there is a call for hot water but retracts when the tap is turned off, the boiler remains lit at all times. I tapped the microswitch a couple of times and it turned off the boiler for a couple of minutes but then it fired up again

Any suggestions or help would be much appreciated!

Many thanks
[/b]

 

[Agile]

There are many different boiler faults.

To correctly diagnose them needs testing.

In the first case a simple resistance test would have shown the sensor to be at fault.

Tony

 

[Theydonites]

Thanks for replying!

Re the resistance test, do you mean pressing the pin in? I'm guessing that the pressure of the water behind it should make it difficult to press or should it be spongey and bounce back?

Thanks,

Danny

 

[Agile]

No! Er.....electronics!

 

[Theydonites]

??

 

[royboywales]

Just found this http://www.kezoki.com/forum/diy-plu...i-boiler-a-27-heating-turns-on-by-itself.html

 

[joolz44]

Hi,

Thanks very much for this link. I too have an Ariston boiler A/23 A/27 which is 13 years old.

The heating was turning itself on and off regularly and I had to turn the entire boiler off and only turn it on when I wanted the heating on. A pain.

I had two engineers in and at last, and several parts later, I replaced the Temp probe. It worked and for a whole year I didn't have the problem again.

However, it has started again. And so, I assume it's the same thing, and I will buy the same part and install it. Same symptoms, same solution, right?

I thought the part would last a bit longer, but hey ho, I'm willing to buy another. Does anyone have any other input? Otherwise i will do this install and let you all know how I got on.

Thanks
Joolz