Ariston SX20 no hot water

[longun]

As the topic says. turn on hot water tap can hear/feel the pump running and see the divertor valve "pin" lift and bridge out the switch but there is no ignition and hence no hot water.
Any help, fault finding suggestions etc. very gratefully received.

 

[Gasguru]

Does the boiler work ok for heating?

Are you sure both microswitches are being operated?

Have a look on the left hand side...does the pin rise on the small brass lump and operate the microswitch?

 

[longun]

Ok now I am confused. just been and tried the ch and the boiler fired up rads started to get hot etc.
Switched off the ch and turned on the hot water tap and boiler worked as normal. IE hot water.
Watched the microswitch to the left and it appears to be being closed correctly.
Any ideas about what might have caused the fault or what may cause it to re-occur?

 

[Gasguru]

Where do I start...

Could be as simple as trapped air in the boiler preventing the differential pressure sensor from operating (the bit on the left).

 

[longun]

OK so would you recommend seeing how it goes and repost if fault re-occurs?
Could you tell me what the diff.pressure sensor does and how to check it.
Many Thanks.

 

[longun]

Same fault re-occured today. Spoke to the tech. people at ariston who said it could be the primary circuit flow switch not making contact due to dirt inside the primary water circuit.
Manually got hold of and operated the microswitch with a hot water tap running and the boiler did fire up, proving the tech. guys diagnosis.

So is it possible to clean out this valve or better to replace it, he also said the primary heat exchanger could have dirt inside it, again is it better to replace or can I clean it out.

Many Thanks in advance.

 

[DP]

Pump might be goosed or HW heat exchanger clogged up.

 

[longun]

Is it possible to clean out the heat exchanger or do I have to fit a new one?

 

[Gasguru]

The diaphragm inside may have perished or weakened. Could also be tight gland seal, dirt inside the small capillaries (or their connections), weak or clogged pump, partial blocked primary or secondary heat exchangers etc.

However in the past I have found it's a partial blockage in the primary heat exchanger flow connection (the washer is a little restrictive AFAIR)...corgi job as combustion chamber related.

Generally a good solid boiler and worth keeping (10 x better than modern Aristons )

 

[longun]

Is it possible to open the flow switch to check the diaphragm.

Could someone please clarify which heat exchanger could be blocked is it the primary one (inside the combustion chamber) or the hot water one (looks like a drum) located next to the diverter valve.

 

[Gasguru]

Pull the device apart but I don't thing the diaphragms are available so you'll need to replace the whole part.

As has been said the fault could be due to several different reasons. Have you checked the auto air vent operates? does the boiler sound free of air?

Start with the easy stuff and work through it. Don't waste your time throwing parts at it unless proven to be faulty.

 

[ChrisR]

Most times these doing this, seems to be due to an ageing pump. Not a standard one.

 

[Agile]

As the pump is more difficult to get, most of the time, the problem is the pump motor start capacitor failing and causing a lack of torque.

Remove the motor start capacitor and measure its value. If its much less than 2 µF then replace it and that should solve the problem. You can often pinch a cap from a failed pump but check the capacitance before changing it.

Tony

 

[longun]

Before I part company with any money I rang the Ariston Tech. line again today verifying that I had intermittant no hot water due to the main flow switch not closing.
I mentioned about the pump and although he said it could be a possibility he was more confident in stating that it would be a partially blocked dhw heat exchanger and/or boiler pipework etc.

So is it possible to clean out the dhw exchanger and if so how/what with?

He also mentioned power flushing? the boiler, is this a recognised solution and if so how much approx. would I expect to pay for a plumber to carry out this work?

Sorry to keep asking but I don't want to waste money buying/paying for parts/labour unneccsarily.

 

[Gasguru]

I'd be very surprised if the secondary heat exchanger was sufficiently blocked to cause the problem...I've not seen any that have caused this particular problem before. In addition these drum type heat ex. have negligable pressure drop...only equivalent to a few meters of pipe.

Forget powerflushing for the moment....it will be very expensive and unlikely to be done properly. Perhaps a weak pump as discussed by others or partial blockage somewhere in the boiler. No easy answer