Potterton Lynx 2 - demand light not illuminating

[kneebs76]

Hi

I've got a lynx 2 which was working fine when I had the CH on, then about an hour later I went to take a shower & no hot water

The CH doesn't heat either now - when I turn a tap on for HW, the water heating light comes on, and there's a quiet 'whirring' within the boiler, but no demand / ignition / flame sequence lights.

When the CH is turned on either by on constant or timed, the same 'whirring' noise is heard but no lights.

I had a problem about a year or so ago where the demand light would occasionally repeatedly flicker on / off quickly, but this sorted itself out when I turned off the mains water supply temporarily for an unrelated issue.

Hopefully someone can give me an idea of what it is & how much it'd cost to repair - I'm quite technically minded, but doubt i'd have the guts to have a go at fixing it myself

Thanks in advance
Mick

 

[twgas]

Have you checked the pressure, should be 1-1·5bar.

 

[kneebs76]

Sorry, forgot to add, yeah, checked pressure & was just under 1 bar - I've topped it up to 1.5 but that's made no difference....

Cheers

 

[hammerswinger]

If you have the manual for the boiler you can follow the fault finding flow chart in the back.

If you haven't got the manual you can get it here:
http://www.partsarena.com/baxi/

(Potterton > Boiler > Lynx 2 > Lynx 2 NG > Installation Instructions)



Cheers.

 

[Agile]

Most likely a failed DHW demand switch.

Tony

 

[kneebs76]

thanks for your replies everyone....

From going through the fault finding diagram 1 & 3 here (towards the end) ... http://www.partsarena.co.uk/baxi/System/DATA/Dx/DS1/installation/2511/I19-2511/I19-2511.htm

....it looks like it's a faulty PCB - the pump works, as I can hear it, and the CH flow switch closes when the CH is turned on, and the DHW flow switch is working as the 'water heating' light comes on when the HW tap is turned on. I've tried flexing the board slightly as I've read of others getting theirs working (albeit temporarily!) (without removing it though), and have checked all the connectors and they seem to be pushed home OK, but it's still the same.

Would this seem logical & correct to you? If so, would you recommend a refurb'd PCB (around £50), or should I stay clear & get a brand new one. Money's a bit tight at the minute lol, so I'd obviously prefer a refurb

thanks again
Mick

 

[Agile]

I would never recommend repaired PCBs!

You say thre system flow switch is activated. But have you actually tried checking it electrically to ensure its making?

Easiest way is to measure the voltage across it and see if that falls to zero when it is closed.

Tony

 

[kneebs76]

Hi Tony,

Yeah mate,I got the multi-meter out and the voltage drops from 24.3 > 0 when closed...

I know what you're saying with regard to repaired PCBs, but the difference of ~£150 appeals to me lol!

My alternative, is, is that I get domestic emergency cover as part of my bank account, but as I've not had it serviced within the last 12 months, I'm not covered . This might be a daft question, but could I get someone to service (but not repair) a faulty boiler, and get the proof of service? Or can it not be serviced without being operational?

Cheers,
Mick

 

[Agile]

Strictly no!

But if you offered to pay someone for a "service" which he did not have to do then I am sure there will be some who will give you the required invoice!

Tony

 

[hammerswinger]

Personally I would take the PCB out & inspect it for cracked solder joints.
Flexing a PCB as you have done will sometimes show up a bad joint but if a joint has been arcing for a while it won't.

I respect Tony's views on reconditioned PCB's & maybe I would advise the same if I were the engineer you had called to fix the problem however, thats not the situation you want your boiler working & if you can get a reconditioned PCB with a warranty for ££££'s cheaper than a new one I would say go for it.

A friend of mine replaced the PCB on his Puma with a reconditioned one a few years ago & it has been fine.


Cheers.

 

[kneebs76]

Well I've took the PCB out & found one or two cracked solder joints but I think this is the problem - it's one of the legs from one of the relays.. Looks like it's been arcing a while....



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[hammerswinger]

I would say that's the boy.

Have you got the gear to repair it?


Cheers.

 

[kneebs76]

I sit writing this from the comfort of my warm flat

Nice, simple 2 minute soldering job...just what I like! I'm just thankful it was the electronic side rather than any plumbing job....I think i'd of had to call in the experts for that!

I'll get it serviced soon, then if it goes again I'm covered

Thanks again folks
Mick

 

[hammerswinger]

The dodgy solder joint on the PCB strikes again.

Great result....Glad you're sorted


Cheers.

 

[Agile]

Solder joints on relay pins often fail.

This is a combination of the mains voltage they operate at which will create arcing and the current they carry of about 1/4 Amp on a pump.

The mechanical movement of the relay probably helps to shake the joint but also when they get older the relay contacts get dirty and that creates more heat which is transferred into the solder joint.

On the Puma PCB there is a different problem. The pin holes in the substrate should be a tight fit so that the pin is supported by the substrate and NOT mechanically supported by the solder joint.

There is a big difference between a DIYer resoldering his own PCB and a professional engineer repairing a customer's boiler. In that case he is fitting an unapproved part which might invalidate his insurance cover.

Also even after repairing an old PCB it is still old and much more likely to fail than a brand new one.

Then there are the real cowboys who fit a repaired PCB and charge for a brand new one! I usually encounter a few of those every year.

Tony