Potterton Lynx 2 hot water problem

[wagggy]

Hi, have a Lynx 2 that i fitted in 1991. I know its now 23 yrs old but it has served me well. Up to 5 yrs ago i had it regurely serviced by a friend of mine who helped me fit it originally, he was a boiler service eng till he passed away.

The problem i have, when running the hot water after about a minute the flame shuts down the demand light goes out but the Water Heating light stays on. after some time the demand light comes back on and boiler relights.

The boiler seems to work ok , but has never done this before.

Could it be the new cct board has been revised to include this function. the old board was Version2 and the new one Version6.

I changed the DHW high temp sensor just in case and tested the flow switch which works fine.

I was a electronics engineer for 40 yrs till i retired, so can deal with most electrical faults. over the years i have repaired the main cct board several times and last dec replaced it for a new one ( New old stock ). i replaced the fan 3 yrs ago. Also about 4 montha ago i replaced the pump for a New Grundfoss one as it started squealing, bearings were shot. not bad over 23 yrs constant use.



Any Ideas please ,

 

[Agile]

We have rules on this forum about not giving advice on gas/combustion issues.

Whilst I cannot be sure but your problem could well be gas related.

To diagnose boiler problems all possibilities have to be investigated and that includes th gas ones.

You have already carried out work on your boiler which we do not advise like replacing the fan.

Consequently I will not be able to advise you apart from calling a competent boiler engineer.

Tony

 

[wagggy]

thanks for responding, obviously if its a gas related problem i will get a boiler technician to deal.

I thought maybe it was related to the new cct board as it didnt do it before and i only noticed it recently whilst being beside the boiler when the demand light went out.

As boiler works ok with heating and hot water i wondered if it was actually a fault. maybe a revision on the cct board to prevent boiler overheating.
That is why i changed the DWH high temp sensor , the old one tested out ok. i compared the resistance with the new one at different temps and they were similar.

 

[Agile]

I don't see why the demand light should go out. That's assuming its following the demand switch.

Have you properly checked that the demand switch is remaining actuated? That means electrically checked!

Tony

 

[wagggy]

I originally thought the flow switch was at fault, put meter on it whilst the demand light went out and it still showed a short, if you disconnect the switch then the Water Heating light goes out.

Its seems the flow switch turns on the water heating light and the control board then activates demand light. Thats why i wondered if the control board is turning off demand when it reaches its temp. It never done this on the old board. Wondering wether the gas regulator is working ok as it doesnt seem to fluctuate the flame like it used to.. You could be right in that it is a gas problem.

 

[Agile]

To allow the burner to stay on the flame size must be modulated down.

You could however measure the voltage applied to the gas valve and see if it varies. It should do that as you slowly turn the hot water temperature control. They usually follow a range of about 6v-14v.

You can also simulate a high hot water temperature by putting a resistance across the hot water sensor. Assuming these are a nominal 10k then say 4.7k should cause the flame to modulate down.

Tony

 

[wagggy]

Tony, I had a look at the gas valve connections and noticed they were dirty and loose, so i cleaned them with contact cleaner and tightened them up.

i then turned boiler back on and ran hot water with meter across the modulator conections. it started at 25v with a full flame. i then slowly turned the water temp down and the voltage dropped to 15v, still flame was at max. i then turned it down a bit more and it dropped to 10v and started jumping from 10v to 6v with the flame going up and down in sync. i left it like this for some time and it didnt stop. i then turned the temp right down and it dropped to 3v and the demand light went out and flame went out.

I then turned the temp slowly up and the voltage went to 25v and the demand light came on and boiler reignited.

It seems to be working a lot better than before. it now seems to modulate if i leave water on for a long time. it must have been a bad connection on the modulator.

Is this the correct procedure for the boiler. thanks again for your help.

 

[Agile]

Most boiler modulate continuously and smoothly.

A few of the old ones only modulated in steps.

There are so few of your type left that I dont remember if it step modded but I would not expect it.

Regardless, most modulate over a smaller voltage swing like the 6v to 14v I suggested before.

In addition the gas valve also has to be set up correctly and that needs an RGI.

Tony

 

[wagggy]

Tony,

The gas valve was setup originally by a corgi engineer when I installed it. And it was last checked about 7 years ago due to another problem ,though it was still within spec then.

Thanks for the pointer with the problem. When I went through other posts on the lynx2 your help certainly stuck out. One was in 2005 so its been some time.

In 2006 I posted a problem and some said buy a new boiler that boiler is called the jinx because its rubbish. I obviously didn't listen and its still going strong 8 years later.

I could have spent thousands replacing it with a condensing boiler which has a lifespan of 8 years and saves me £90 a year in fuel. How is that saving the planet. Biggest government con going.

My Bosch washing machine is 15 yrs old and still perfect. Replaced 2 heater elements , 1 set of brushes , and I regularly clean the pipes and pump out which is the main problem with them. According to Bosch they are only designed last 5 yrs and then you should buy a new machine.

If everything lasted forever though we would be out of a job. I offset the balance if I can help it..

Thanks again

Alex