Potterton Lynx 2 problem

[Panoramic]

Hi, I am sure there have been plenty of questions about these boliers before. I am hoping there is an expert lurking somewhere around here.

The prroblem is this, hot water;

Turn on tap, bolier fires up perfectly but switches off after about 2 minutes. the pressure gauge is on about 1.5 bar, if I increase the pressure using the filling loop the bolier comes back on, then goes off, a bit more pressure and it comes on again. Obviously I can't keep doing this. Also if I let all the water out of the system via the PRV, then re-fill it, it will then waork again fine for 2 minutes then we are back to sqaure one!

I am thinking DHW flow switch or some kind of heat cut out? which powuld explain why it works if i empty the hot water out and fill it wioth cold?

Any ideas or suggestions would be appreciated.

Thanks.

 

[MeldrewsMate]

Lynx 2 ...that's an old 'un alright. I'll have to ask the wife on this one (wives are the only ones who can remember problems from years ago, and recall them instantly!).

Hazy memories only, but here goes...
Single PCB behind a hinged flap I think, and electric (Honeywell?) diverter valve?

1. Does it repeat the process on heating duty? If so take a closer look at the pump, it could have failed, but two minutes is a little too long to burn with no circulation.
Clearly two minutes, like "two seconds", is rarely 120 seconds. if the symptom occurs at about 30 seconds, then it puts a whole new slant on the fault.
2. There may be a temperature sensor (again from memory only) on the pipe between the heat exchanger outlet and the secondary heat exchanger. If that's failing it could cause this type of problem.
3. Finally, if it's the main PCB at fault you may have great difficulty finding a replacement - I think I have one in the attic, so PM me if you need one.

More symptoms needed beyond that...MM

 

[Panoramic]

Hi Thanks for the response,

Yes you are right PCB on hinged flap, honeywell diverter.


I can't coment about the heating as it's currently not in use. I have a rad off and the pipework capped off whilst I refurbish the bathroom. It has been off for about 6 weeks and the DHW water has ben working fine until now.


Next time I have the bolier working I will time how lond it stays on for.

Thanks for the PCB offer, I replaced the current one about 4 years ago. Will let you know.

 

[gasafengineer]

Temporarily link out water pressure switch.

 

[Panoramic]

Thanks gas. Could you possibly give me a little more detail?

Thanks for the help.

 

[gasafengineer]

Could be a number of issues , if hose to expansion vessel is partially blocked water pressure upon filling will suddenly rise making the switch contacts @ water pressure switch , depending on how restricted the blockage is the water pressure will slowly be released back into vessel hence breaking the contacts @ water pressure switch & shutting the boiler off.

Check for PRV letting by , also check expansion vessel hasn't depleted , if re-pressurising vessel then blockage to vessel must be cleared , also make sure drain off/other is open when recharging vessel.

For a quick test pull wires off water pressure switch (two) & link them out. (join together)

 

[Panoramic]

Hi Gas,

pressure vessel was replced about 6 months ago.

I have tried linking out the cetral heating prerssure switch and the DHW flow switch and it has made no difference.

When the hot waer tap is turned on I can hear a "click" from the DHW pressure switch.

 

[Panoramic]

Now when link up yhr toe central heating pressure switch wires I am gettind "low sysytem pressure" light on, when I connect them back to the pressure switch I get nothing.

 

[Beerlover]

Before you spend too much time and money, isn't it about time to bury this dog of a boiler? Plenty of Pumas have been buried, and they were 4 times better.

This was the boiler that sank Potterton's name and allowed Baxi (the French partner) to get control.

Unlike the Murphys I am bitter

 

[Agile]

The pressure switch works "backwards" it seems. The Puma did that too so its their bad idea of a design feature.

Just because the EXV was replaced it does not mean that the communication pipe is not blocked.

Does it work normally when the pressure switch connections are just removed?

This is a very simple boiler and pretty reliable if you forget poor joints on the PCB.

They are about 17 years old now but still repairable!

Tony

 

[Panoramic]

Thanks Tony.

I have disconnected the two wires from the pressure switch and connected them to a normal on off switch, the boiler is working a lot better and staying on a lot longer. I think some of the problem is the thing is full of air but I am gradually getting it out.

You are right these boliers are pretty reliable this thing is nearly 20 years old and has had one PCB and one pressure vessel so far.
The problem these days is there is a lack of tradesmen with the skill and knowledge to repair anything. All you get is some chav in a white van. Taking one look with out even taking the cover off the bolier and sayin "nah mate, you want to get a new one, only £3,000 cash"

 

[Tibbot]

The problem these days is there is a lack of tradesmen with the skill and knowledge to repair anything. All you get is some chav in a white van. Taking one look with out even taking the cover off the bolier and sayin "nah mate, you want to get a new one, only £3,000 cash"

Just because it's repairable doesn't always mean it's economically worthwhile for someone to take it on (specialist or not). Why is the heating industry expected to wet nurse something that's reached double it's life expectancy when other faulty household goods are happily thrown as soon as their warranty expires?

 

[Agile]

Its also possible the pressure gauge tube is partially blocked.

Do you have evidence that its OK ? Like going down to zero when its empty?

I am one of the few who will repair these boilers but I do agree that they are mostly well due for replacement.

The one I have recently worked on is for a lovely Indian lady and she does not work although well qualified and so does not have much money to replace ( or so she says ).

Tony

 

[SwissToni]

Their is an air flow sensor at the top of the boiler which can become oxidized, carefully remove and clean contacts. if the problem persists it may be the fan is semi seizing strip down and lubricate this should resolve the issues.