potterton lynx problem

[puzzledplumber]

Hi everyone. I have a problem with a Potterton Lynx Electronic Combi boiler. Instead of the normal ignition sequence, the system goes straight to high flame light on, with no attempt at lighting. I have changed the sequence and modulating boards with no luck. The air flow sensor appears ok. Any ideas anyone? Many thanks

PP

 

[Agile]

I would ask what you changed the sequence board into?

What have you tested so far and what were the resistance measurements obtained?

How did you come to the conclusion the air flow sensor "appears OK" ?

It sounds like an interesting fault, the kind that I like to work on!

Tony Glazier

 

[puzzledplumber]

Tony thanks for the prompt reply.

The sequence board was changed into another identical board from the local supplier, allegedly in full working order.

Tests so far. Pump working but fan not. Have shorted across water flow switch but no luck. Air flow sensor checks out at around 1 - 2 ohms. My DMM only has a resolution of 1 ohm so cannot check any more accurately than that, but would guess that if it develops a fault it is either short circuit or open circuit. Any thoughts that you have would be much much appreciated.

Does anyone have a link to a set of circuit diagrams?

 

[Agile]

"""changed into another identical board from the local supplier, allegedly in full working order."""

That worries me because it sounds as if you are not accustomed to fitting new parts and go to places like Adlink who do not have facilities to properly test them.

You say the fan is not working! Have you checked the resistance? Have you checked to see if voltage is applied to it? Have you powered it from a plug lead to independently checked it?

If the fan is working but no power is being applied then the system flow switch needs to operate first. Its a common failure point. Have you measured the voltage across it with the pump on/off ? have you inspected the pump impeller? Have you removed the flow switch and inspected/cleaned the paddle?

It does not sound quite so interesting now!

Tony

 

[puzzledplumber]

It was a reconditioned board bought from a reputable local supplier and sold with a guarantee. Also one of my neighbours is in the trade and he has loaned me 2 additional boards, with the same result.

As regards the fan, there is no voltage on pins 23 and 24 of the distribution board and running 240v externally gets the fan working.

The flow switch seems to work. I have measured the continuity with the pump running and off. The continuity goes from O/C to S/C as you would expect.

Hope this has got your interest back

 

[croydoncorgi]

Have a look at the fault-finding sequencein the MI.
Youll find it at http://www.partsarena.net/gas/default.htm
If the flowswitch is OK, the next thing to check is the DHW Limit stat.

 

[geoff@cetltd]

"""changed into another identical board from the local supplier, allegedly in full working order."""

That worries me because it sounds as if you are not accustomed to fitting new parts and go to places like Adlink who do not have facilities to properly test them.

Tony

Both Adlink and ourselves DO have facilities to properly test these boards, they are not that complicated. Possibly the difference is that I do test them properly and they don't any more. Considering the price of new pcbs for a Lynx, a recon is the only sensible option on a boiler of this age

ISTR from talking to one of my employees, that the resistance given by Potterton in the manual can't always be relied on to guarantee a working air flow sensor. He always used to carry a known working one around with him for such occasions. What happens if you blow air through a pipe directly on to the AFS ?

 

[Agile]

The resistance is only about 1.2 ohms as measured at the pcb end.

A much better way to check the operation is how the pcb does it by measuring the voltage across those pins.

Problem is most people forget to replace the combustion cover and wonder why the boiler does not work !!!

That cannot be the problem here because the fan starts before the pcb looks at that sensor.

Tony

 

[puzzledplumber]

Thanks for all your feedback so far. Tried the link as suggested by CC, but that just takes me to the Potterton manual which I already have a paper copy of. Unfortunately it does not contain any circuit diagrams, just flow diagrams and logic sequences. The fault finding sequence doesn't take into account the scenario of the high flame light being on but the gas not lit. And of course if the sequence board thinks that the flame is on, then it won't schedule the ignition sequence etc.

Have checked the DHW thermostat as suggested, but that measures a S/C which the book says is correct in the cold and unenergised state.

If anyone can point me to a link to the full pcb circuit diagrams that would really help, otherwise I will have to try to trace it out manually.
Although it is not a complicated pcb, it will be a time consuming exercise.

 

[geoff@cetltd]

I don't think you'll find a complete circuit diagram for any boiler pcb (with a few exceptoins), and I'm not really sure what you expect to achieve by getting one

 

[Agile]

Yopu should be able to manage with the functional operational diagram from that link.

It shows the links before the fan being:-

Summer/winter switch

on/off switch

Shut down relay

RLA to power fan.

The problem might be the "shut down relay which I assume is a lockout relay.

You need to follow that diagram and tell us where the power fails.

Where abouts in the country are you?

Tony

 

[Softus]

Where abouts in the country are you?

Are you short of work again Agile?

 

[Agile]

Softus, again you have contributed nothing to this enquiry!

If you only read it you would see that this is an industry colleague who is repairing the boiler for his customer.

It sounds as if its you who is short of work!

Tony

 

[Softus]

Softus, again you have contributed nothing to this enquiry!

Not again, to be precise, because that was my first post on this topic.

If you only read it you would see that this is an industry colleague who is repairing the boiler for his customer.

I had read it; I've now read it again, and I can't find the part that says you were going to do some work for nothing.

It sounds as if its you who is short of work

I'm not. I have so much work that I don't need to advertise - I never have and I don't suppose I ever will.

 

[Agile]

Agile wrote:

"""Softus, again you have contributed nothing to this enquiry!"""

Softus replied:

"""Not again, to be precise, because that was my first post on this topic."""

When I said "again" I meant that again across all the postings which you make you only disect and comment without saying anything relevant to to original topic.

Its obvious to everyone else, without me having to say it, that I am giving advice to help my industry colleague fix the boiler and I have no intention of charging for that.

Tony