Baxi wm70 4pf PCB

[jcochr]

My boiler has stopped working! The pump runs and the system clicks but no spark/ignition. The Light for cover number one is on and number two is flashing.

I checked the PCB and there is a blown 3 watt resistor in the corner called R10. Unfortunately, it is all black and I can't see the resistance code.

Please help if you know what resistor this is or if you have any suggestions. It is the weekend and cold with no open suppliers....

James

 

[tamz]

Better to look out the hot water bottle until monday

 

[Agile]

If the resistor has blown then its because something else has failed and created an overload.

Thats a PCB we dont keep in stock so I cannot look and see the value and I dont have the interconnection chart to see what it does as a pointer to what has failed.

Have you actually measured the value of the resistor? Just because the paint has burnt off it does not necessarily mean the resistor has actually failed.

Tony

 

[jcochr]

If the resistor has blown then its because something else has failed and created an overload.

Our thoughts also - the question is what...

Thats a PCB we dont keep in stock so I cannot look and see the value and I dont have the interconnection chart to see what it does as a pointer to what has failed.
I am pretty sure the first two bars are Blue and Grey which makes it probably 68 Ohms rather than 680 ohms or more.

Have you actually measured the value of the resistor? Just because the paint has burnt off it does not necessarily mean the resistor has actually failed.

Yes- also checked it at the shop for resistors. Now that I have taken in off the board I can see the second stripe is grey.

Do I need to make sure the replacement goes high when it fails? I read a post of yours in Gas-news that said that these manufacturers use resistors on pcb boards as fuses...

It would be perfect if getting a new resistor for this board brought the whole boiler back to life but it seems a long shot. Thinking of the cause - the only changes recently made have been turning down the water temperature to avoid burning the kids and the wife turning on both the hot water and central heating at the same time. Never had any other problems...

Tony[/quote]

 

[Agile]

Carbon resistors naturally tend to go low resistance when hot.

Its only the odd manufacturer which uses fusible resistors as a protection, usually in series with gas valves and fans etc.

You seem hell bent on replacing that resistor although you do seem to recognise the logic of what I have told you.

Why not follow on the leads that I have given you to trace the circuitry to see what the resistor actually does?

Tony

 

[jcochr]

Changed resistor for a slightly higher watt value ie 2 watt (probably). System has restarted and all seems fine.

If it keeps going that is pretty good for a 25p resistor and a trip to town.

Fingers Crossed but all seems well

 

[jcochr]

A theory: All these old Baxi boilers have this fault with an insufficient resistor that eventually wears out and many people pay for new or re-conditioned control boards that you see for sale on eBay etc. These recon control boards look the same except for this resistor which has been moved and replaced with a larger version.

The resultant effects of this problem must cost lots with the labour and call out charges to unsuspecting clients.

No one will say this as lots of people make money going out to fit new circuit boards or anything else they can see as a "cause". They will also tell you not to investigate but get someone from the trade to diagnose the system etc.

Perhaps I am just an old cynic!

 

[Happyplumber]

You are an old cynic! fortunately as you are working on your own boiler then its fine,but we have to adhere to the regulations to ply our trade.

It has been seen as rule,and not us risking our livelihood by repairing PCBs,yes just like yourself we have some electronic knowledge and can repair alot faults,but then manufacturer will carry no warranty on these repaired items.

Thats why when we need a new new pcb we will buy brand,then if anything goes wrong the RGI is not to blame

 

[jcochr]

Well it has been a good 18 months since this issue and I had a problem with my zone valve. I got a plumber in to have a look and he replaced the valve but put it in the opposite way round to previously. After a minute of operation he left and when I tested it again, it had stopped working. There was a similar relay clicking problem with no ignition (or spark apparently) in the boiler although there seemed to be a weak spark on the board.

Any suggestions? Does it matter if you plumb the valve in the wrong way round - it is a two way and directs the water to the CH when powered open. Closed it runs to the HW.

Thanks for any suggestions.

James

 

[Agile]

I am a little confused by your posting! Do you mean your boiler has failed again?

Two way valves have a water direction arrow on the side. You can see the arrow on the pump and follow that direction towards the valve and see if the valve continues that direction.

If he has put it in backwards CALL HIM BACK to correct it.

The sealing ball is pushed back AGAINST the flow direction when correctly fitted.

If fitted wrongly the flow pushes the ball against the seat and closes the valve with a sharp stop and this can make the pipework thump or bang.

Dont assume its wrong now! You check it. It MIGHT have been wrongly fitted before!

Tony Glazier

 

[jcochr]

Tony,

Thanks. I am pretty sure that it is plumbed in the wrong way round because:

a: The pump also has an arrow pointing up towards the boiler and now so is the valve whereas previously the valve arrow was pointing down. I doubt all the 22mm pipes head towards the boiler as they must fit on a circuit. I would expect the pump to have been plumbed correctly.

b: The previous way it had been set up did not have any issues for about x years- where x may be .

I did not explain the current problem very well - the spark now seems very weak whereas was fine before the work was done - it can be seen on the board but not in the boiler and the boiler is now not lighting. I can't get a spark when I remove some of the insulation from the HT lead - previously to the visit it lit fine.

Funny, I have spent money on a plumber and a new valve with a boiler that now does not work at all and is likely plumbed in the wrong way round. I should have done it myself/checked more carefully before he left. I also wonder how the new problem occurred and what the new problem is - the resistor that previously blew is not blackened and reads 70 ohms ok with a meter. The plumber barely seemed to touch the boiler although I did not watch all the time.

I am considering getting a new sequencing board as they are cheap off ebay and may solve/diagnose the problem. I have contacted the plumber and he says it does not matter which way you plumb the valve/it must have been wrong before.

James

 

[jcochr]

Sorted the problem - there was dust on the electrode and spark point. Had to clean both in the end. Should have thought of that...

He turned the valve round also.

The end (for a while... as I think the board is not producing the spark it once was)