Potterton Lynx Combi failure to ignite

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First just to say I'm new to the site and thanks for this site and for all the top advice and responses I've read in trying to work out what my bolier's prob is.

My aged Potterton Lynx (in the house when I bought it 10yrs ago) has started to sulk. 3 or 4 times in the last month, it's failed to ignite when either CH or DHW are demanded.

The Demand light lights and there's sound (like water flowing through) from the boiler, but no slight clicking or buzzing sounds (which normally happen just before the ignition light comes on), no ignition light and therefore no heat.

It's happened in the day & evening, and both while the CH has been off and running on timer (so prob not be connected to overheating?). Both CH and DHW controls are set to around "10 o Clock" - which is medium.

If CH off, opening hot tap illuminates the Demand light, but there's no ignition. If CH is on via timer, it's must have either started heating at first but then failed to ignite to maintain temp at some point, or just never ignited, so the demand light is on, the CH pump is running, but no ignition or heat.

First time, not knowing there was no pilot light, I figured it was just the pilot blowing out, so cycled the mains power to the boiler off and on a few times with the CH and/or DHW running, and after a few goes, it fired up and then worked consistently for a while. Second time, it came back with a power cycle or three and again ran for several days with no prob.

Yesterday, heating failed to heat in the morning, and couldn't get HW demand to ignite boiler either. Tried the power off n on several times, but to no avail. I left the boiler powered up and with the CH running (no ignition) while I went to seek advice. Then, around 45mins later, all by itself the boiler fired up.

I'm planning to replace the boiler anyway in the not too distant, but right now could use any advice on what the prob might be so I can keep this one working for another few months. From reading other posts, could it be the PCB? Or is it just the ignition device which is failing to spark? Or is it some temperature sensor problem causing the boiler to cut out?

Any help gratefully received.

Oh and Happy New Year!

Andy
 
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If it only happens occasionally then it can be difficult to fix!

These are getting a little old now but are still OK boilers when they are working.

If I remember correctly there may be a system flow switch which is required to be activated before the boiler proceeds to the ignition stage.

These get dirty and sluggish with age and if I remember correctly this may well be your problem.

Are you able to measure the voltage across it to see if it operates? You may have to watch it for a long time before your fault reappears!

Tony
 
Common fault on lynx 1. It has 3 boards the mother board ,the modulating board and a full sequence board this is the one that contols the ignition of the boiler and is the faulty one that you need to change cost approx£100
 
Hi,
I have had a similar if not the same problem.
There are noises like air coming out and my plumber stated it would be the sensors but as the heating / hot water was not available that would mean both sensors going at the same time, highly improbable.
I replaced one of them and it made no difference.

I proceeded to replace PCB and when I was moving it noticed that the boiler started working when horizontal but not when vertical. Why, I then noticed the the black box thing at the right which is screwed to the PCB had one screw bolt loose with missing nut and the other was loose.

So in the horizontal position gravity was making the contacts , but vertically it would be hanging off.

I duly tightened this up, found the missing nut in the boiler pcb tray.

Everything works...........

I hope this is useful for someone else.
 
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Of course not although I thought that could be surmised from the way I had written it.

For each look at the pcb all power was off, but at each stage i would reapply power and test.

So when the pcb was in the horizontal position with power off I wriggled the socket smaller circuit boards to see if they were loose or could be removed. I found them secure, and then tested the system. Wow it was working, I thought if I put this back as it was it probably won't work so, as it was not working before when vertical so I got to thinking what has changed.
Horizontal against vertical, which one wins and why.

So with power off I'll look under the board to see if any cracked joints are visible or something to do with movement, and when looking I noticed the black thing was loose. Ok I tightened it up and found the nut was off one of the corners, and sorted that.

Ok, lets see if its still working horizontally, yes.

Well now I have changed something and it looks plausable to be this, so power off put back together.

Fire up, its working.........
test hot taps, yes
watch - see how long its going, radiators working and it switched off when hot. Is that it, no a bit more waiting and it switched back on.

Thats history - two days ago working since.
 
To continue, I didn't replace the PCB.
All I did was tighten black box thingy on top of it.

I also replaced one of the sensors (Thermister)
firsty the ch one with a new one, no difference, so then the DHW one with that same new one. Still no difference.

As there is a sensor for DHW and also one for CH the clue is that the boiler was doing the flashing lights thing for both so both would have to have gone bad. For that to happen is possible but highly unlikely at the same time. Think of the chance of your car having two punctures at the same time, its just so unlikely.
 

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