Ariston EuroCombi cycling

[robscot]

Hi all & Happy New Year,
Looking for advice about an Ariston EuroCombi A27 which is giving alternating hot&cold water and central heating.

The burners fire from a cold-start, but once it has been on for a minute or so, everything (pump+fan+burners) stops dead. A few seconds later it starts whirring again, the burners fire after around 20 seconds, it all stops dead again around 35 seconds and the cycle repeats.
The effect is that DHW goes between freezing and very hot water - the hot taps and shower keep cycling between hot & cold.
CH radiators get warm, but if you touch the CH feed pipe coming out of the boiler you can feel it going hot & cold with each cycle - same as DHW.

Two plumbers have tried to fix it, starting with replacing the Air Pressure Switch (there was another fault a month ago - it wasn't starting until given a thump), cleaning the venturi and the fan, cleaning a temperature sensor and replacing the bottom-right control PCB (pump relays etc.). They just put X800 through the CH system and that doesn't seem to have helped.

I'd be v.grateful for any ideas on what could cause the boiler cycling.
Odd thing is I didn't notice it doing the cycling until the other fault (with the APS) was fixed - showers were cold until you gave it a thump... Ah, Ariston

 

[Boilerman2]

I'm not a member of the Ariston fan club I'm afraid!

however if this problem started after the APS was fitted it is POSSIBLE that this could be the source of the problem, if a generic part was fitted it may not be correctly set, however only a RGI can make any adjustment to this it is NOT for DIY !

 

[robscot]

Thx for the reply. No worries - won't be attempting any DIY. Can't say I'm a member of the Ariston fan club either - cold showers have worn a bit thin over the festive period.

Another forum had an Ariston cycling and said it could be "the plate HE is blocked with sludge/crap on the system side"- recommended removing and cleaning... does a blocked HE also sound possible in this case?

 

[Agile]

I cannot totally visualise your model but let me assume that its a later one with a black motor diverter valve actuator.

It sounds as if EITHER:-

The diverter valve is faulty and cycling instead of stopping. If so this will be at EXACTLY the same number of seconds and probably about 10 seconds. Thats rare but possible.

The DHW demand switch is dropping out and sends back into the CH mode. This might not happen if you increase the DHW flow rate by turning on all the hot taps.

Apart from being there at your boiler its not possible for me to come to any firm conclusion and those suggestions are only possible causes.

Unfortunately you have been the victim of "plumbers" who obviously did not have much clue of how to diagnose boiler faults.

You would be better off with a boiler engineer instead of a plumber!

Tony Glazier

 

[DP]

Throwing parts at the boiler and blindly trying things and hopeing the fault will be cured can be a little disheartening for the end user.

While the boiler is quirky the way some of the components are fitted, it is still many times better than a lot of boilers.

If the boiler is short cycling for both HW and CH, it has to be a component that is common to both. Doubt it will be the HW heat exchanger as boiler is behaving badly during CH too. Fact that the fault is present, locating should not be too difficult.

Doubt the main HE will be scaled up, not in Glasgow, unless the previous boiler turned the system water to black broth.

 

[nickso]

A27 is an old turd. Think it uses the same left/right manifolds as the jaguars and maxins. Diverter duties are done with the flow differential and diaphragm.

I Agree with Danny, primary heat exchanger or the thermistor is always worth checking on Aristons. Is it noisy?

 

[nickso]

Odd thing is I didn't notice it doing the cycling until the other fault (with the APS) was fixed

Worth checking that's been done properly too.

 

[Agile]

Based on Nickso's confirmation that this model does not have the motorised diverter valve than a faulty motor is not a possibility.

But the possibility of the diverter valve dropping out is still a possibility. Its easy to see on that model and you need to watch that the pin on the right of the left hand hydro block is staying out ( to the right ) and not retracting.

I expect that it will be OK and in that case then there is a strong possibility that the replacement of the air switch was not done correctly or with the correct component.

Those aspects do require a competent gas engineer though so I cannot give DIY advice about it.

Its a very simple and quite straightforward model ( other Aristons are not ) and DP above couldbe called to sort it out for you in Glasgow. Either contact him through his profile or locally as Rannoch Services.

Tony

 

[robscot]

Thanks v.much for your responses.

>>if a generic part was fitted it may not be correctly set

I've got a friendly boiler engineer coming out this week so I'll ask him to check the APS was fitted properly by the original plumber.


>> diverter valve is faulty and cycling instead of stopping. If so this
>> will be at EXACTLY the same number of seconds and probably
>> about 10 seconds. Thats rare but possible.

It's more like 15 seconds till the burner lights, and then 30seconds burn till it all 'shuts down' for a few seconds and then repeats.


>> The DHW demand switch is dropping out and sends back into
>> the CH mode. This might not happen if you increase the DHW
>> flow rate by turning on all the hot taps.

I'll check that out again... I think we tried that 'tho, and don't remember it helping.


>>If the boiler is short cycling for both HW and CH, it has to be a component
>>that is common to both. Doubt it will be the HW heat exchanger as boiler
>>is behaving badly during CH too.

Yes, affects both CH and HW in same way.


>>watch that the pin on the right of the left hand hydro block
>> is staying out ( to the right ) and not retracting

It seems to be staying out OK.


>>primary heat exchanger or the thermistor is always worth
>>checking on Aristons. Is it noisy?

Hmm, not noticed any more noise than when it was working fine


>> >> didn't notice it doing the cycling until the other fault (with the APS) was fixed
>> Worth checking that's been done properly



I will get that APS checked out by the engineer who is hopefully coming this week...

Actually, one thing I'm remembering now is that the plumber noticed that when he ran the boiler with the internal cover off (the silver panel which covers the burners, APS and fan) then it didn't do the cycling... it stayed on all the time.
He said it was unsafe to run it with the cover off, and thought that the pump stopping after each cold-to-burning-hot cycle indicated a board/timing PCB fault.

Would the "OK with cover off" solution indicate an APS problem after all?

Thanks again for your advice.

 

[nickso]

APS fault then. Get your man to check it out, shouldn't take him long with an obvious hint like that.

 

[Agile]

If its OK with case off, that that indicates a fan/APS problem.

He does not have to check that it is "correctly fitted" !

He has to check that its is the correct specification!

He has to check that the applied air pressure is correct!

Only a registered gas engineer should even open the combustion chamber.

Tony

 

[nickso]

Sorry, should have said, APS or related fault, not necessarily the APS, in fact I find it rarely is.

 

[robscot]

Hi again, couldn't get boiler engineer to come out this week, but I've passed on your suggestions and spoken to him on the 'phone.
He has visited previously to change the pump-relay PCB so he has inspected the work done by the previous plumber(s).

He is still of the opinion that it's a thermostat/PCB or related fault, and is recommending a new boiler.

>> If its OK with case off, that that indicates a fan/APS problem.
>> He does not have to check that it is "correctly fitted" !
>> He has to check that its is the correct specification!
>> He has to check that the applied air pressure is correct!

The old APS was marked "Honeywell C6065FH1136:2 9920D",
the new APS was marked "Honeywell C6065FH1128:2 F4101" and "Ariston Part.No. 571652" (as in the service manual)

re: pump...

He said that the "pump powering down" in the middle of the cycle wasn't consistent with a wrongly-fitted APS. The pump should still spin?
(The burners are on for a while and then the burners, pump and fan all stop for a few seconds, then the cycle starts again with fan+pump no burners, then burners kick in for a while, all cut off, and cycle repeats...)

I mentioned the "working with cover off" would indicate APS, and he said that the cover-off condition changed several factors and might affect the thermostat etc. so it wasn't changing his mind on the board/thermostat issue vs. APS issue.

I'm still thinking the air-pressure system but didn't want to tell him his job... is he right about that 'pump powering down' indicating something else?

 

[DP]

He has visited previously to change the pump-relay PCB so he has inspected the work done by the previous plumber(s).

Someone who sees a boiler replacement will not have will power or yearning to fix a boiler fault. Some of what you write make no sense at all.

A thermostat comes into play ONCE burner has fired and heat is being generated and then CONTROLLED by the thermostat.

If I remember correctly, this boiler does does not have mechanical thermostats- this action is electronic and checking of sensors is first thing a determined heating engineer would embark on.

I do not understand the term 'pump- relay PCB' A PCB will have relays on it, one of which will run a pump by operating a relay, so cannot see how desribed action could have been made.

 

[robscot]

Thanks, please excuse the incorrect terminology as I am not a boiler engineer.

>> He is still of the opinion that it's a thermostat/PCB
>>or related fault, and is recommending a new boiler.

When I said "thermostat" I should have said "temperature sensor" (the CHW temp probe inside the Ariston was already checked by the first plumber who said it was just 'dirty').


>>I do not understand the term 'pump- relay PCB'
>>A PCB will have relays on it, one of which will run
>>a pump by operating a relay, so cannot see how
>>desribed action could have been made.

There are two PCBs in this Ariston EuroCombi A27/MFFI, the bottom-right one which apparently operates the pump (via a relay) was already replaced by this boiler engineer. (Ariston Part No. 952975)


>>A thermostat comes into play ONCE burner has fired
>>and heat is being generated and then CONTROLLED
>>by the thermostat.


Understood. What internal sensor malfunction (APS, temp-sensor etc.) is most likely to cause a pump to stop completely between hot-cold cycles? Or is that a 'how long is a piece of string' question...?

My boiler engineer seemed to think the pump stopping was v.important to note... showing that the hot-cold cycling wasn't related to the APS or pressure system, and could be a PCB fault.

There are no warning lights appearing on the front-panel.

You may be correct about 'will power or yearning' to fix this fault - the first plumber also recommended a new boiler.