GlowWorm 30cxi boiler. Now NO need to buy replacement! :)

[muggles]

You might have missed a trick here but it's still worth a look - if the boiler was faulty when you bought the house, you can prove it, and it wasn't declared by the previous owners then you have a valid claim against them. Unfortunately with five months having gone by you might have missed the boat on that one but it's probably worth giving it a go

 

[Agile]

The earlier boilers and many other makes used a 230v motor with limit changeover switches where the PCB just supplied to either of the direction connections.

Yours is obviously the fairly recent newer type which from a repair point of view is much more difficult.

I am surprised it uses a current monitoring design as that's so over complicated. The Vaillant boiler just sends the number of pulses that it needs to travel which is much simpler but even so that part of the PCB can still fail.

Some others here know all about this but the display PCB, as on many other boilers, defines boiler model etc. and does much more than just act as a dumb display!

Now you can see all the problems boiler engineers have to contend with.

Unlike Worcester boilers, I think there is no kit and you have to order each "O" ring separately for your model.

Tony

 

[underwurlde]

You might have missed a trick here but it's still worth a look - if the boiler was faulty when you bought the house, you can prove it, and it wasn't declared by the previous owners then you have a valid claim against them. Unfortunately with five months having gone by you might have missed the boat on that one but it's probably worth giving it a go

That IS a thought that has occured to me. They damn-well knew their boiler was f-ed, of course they did! AND went out of thier way to dismiss these problems, even to the point of stating that they were quite willing to sell the property to someone else two MONTHS into the purchase, their point being that my solicitor (who is also a close personal friend) was being 'unnecessarily pedantic'.

To circumvent the installation issues (no certificate of installation available, even though they said one was provided at the time it was installed) they agreed to take out an indemnity insurance policy for me such that my mortgage company could then agree to lend. That policy of course does not cover this problem!

Heads up therefore for anyone reading this!

Andy

 

[underwurlde]

The earlier boilers and many other makes used a 230v motor with limit changeover switches where the PCB just supplied to either of the direction connections.

That was exactly what I was expecting to see. Imagine my surprise then to see such a wierd motor controlling the diverter valve with no 'obvious' means of knowing where it was.

Yours is obviously the fairly recent newer type which from a repair point of view is much more difficult.

Yep!

I am surprised it uses a current monitoring design as that's so over complicated. The Vaillant boiler just sends the number of pulses that it needs to travel which is much simpler but even so that part of the PCB can still fail.

Maybe, but how does the control board know where the actual position of the actuator is? I'm really hoping to learn something here as it is a mystery to me other than seeing current monitoring circuitry which I was assuming to be end-stop detection and prevention of over-current situations (which did nothing to it would appear to prevent damage).

Some others here know all about this but the display PCB, as on many other boilers, defines boiler model etc. and does much more than just act as a dumb display!

Now you can see all the problems boiler engineers have to contend with.

Indeed! Very strange designs. Very strange!

Unlike Worcester boilers, I think there is no kit and you have to order each "O" ring separately for your model.

Didn't think so as I could find no such kits on eBay. More faffing about then!

thank you again Mr. Agile!

 

[Agile]

Maybe, but how does the control board know where the actual position of the actuator is? I'm really hoping to learn something here as it is a mystery to me other than seeing current monitoring circuitry which I was assuming to be end-stop detection and prevention of over-current situations (which did nothing to it would appear to prevent damage).

thank you again Mr. Agile!

In relation to the Vaillant method:-

The PCB does not need to "know" where the diverter is. It sends the movement signal and "assumes" that it has moved !

But to prevent errors when first switched on it moves it to heating and then back to hot water ( because it does not know where it was ! )

The current increase when stalled will be very little higher as its primarily determined by the DC resistance.



I am a little surprised that on your model there is apparently enough increase to be useful for monitoring when it has reached the end.

Tony

 

[underwurlde]

In relation to the Vaillant method:-

The PCB does not need to "know" where the diverter is. It sends the movement signal and "assumes" that it has moved !

But to prevent errors when first switched on it moves it to heating and then back to hot water ( because it does not know where it was ! )

...

Yes! That is why my boiler appears to do: Upon first powering up, in goes the actuator (for a set period of time) then back out it comes. (You can hear it buzzing aka straining if the actuator is already at the end of it's travel, but that set period of time does not appear to change). Hence from then on it 'assumes' it knows where it is. Simple, but prone to error of course if there are problems with a stuck actuator.

If there are problems with assumed actuator position being 'guessed' as wrong by the system, then one will see seemingly unrelated issues with heating / DHW (as happened to me), thus making diagnosis of the resulting problems 'interesting'.

You live and learn!

 

[Agile]

For a boiler engineer, sticking diverter valves are a very common experience as the Vaillant ones first fitted 12 years ago were seriously liable to sticking.

The design was soon modified with a rugby shaped ball and larger holes at the side. They only occasionally stick!

I would expect yours to also use the set number of pulses like the Vaillant one. Although you seemed to think it was current sensing instead.

Since the Vaillant one regularly stalls it cannot result in much increase in current as that does not usually result in PCB failure.

Tony

 

[underwurlde]

...

I would expect yours to also use the set number of pulses like the Vaillant one. Although you seemed to think it was current sensing instead.

Since the Vaillant one regularly stalls it cannot result in much increase in current as that does not usually result in PCB failure.

Hmmm. Thus far for my thinking: Guesswork based purely by me looking at the schematic and then applying what I would do if I were writing the control code. You have now educated my thinking to a simpler model.

As to WHY a stalled actuator (may?) cause component failure on the PCB, who knows - could be anything until I probe further. All I can say is something HAS failed with regards to the control of that actuator.

Current monitoring could be there for short ciruit conditions on the wiring etc to the actuator motor, although my brain still sees it as also being there for current monitoring for other reasons.

Thanks again chap,

Andy

 

[Agile]

Boiler PCB designers seem to take pleasure in making their designs totally intolerant to any overload so that they fail as often as possible!

Many of the older designs used to have a VDR on the mains input to guard against spikes.

Also some of them also had a current limiting PTC thermistor so that with any overcurrent it would limit the current and reset automatically when depowered for a few minutes!

Tony

 

[underwurlde]

The design of this PCB has common-mode mains filtering and a VDR driving quite an elaborate Switched Mode power supply to generate 24V DC (from which 5V is derived using a simple 5V linear regualtor). No issues there then, but other than a schematic, I have not looked at it further.

Back to my faulty PCB.

It appears that all 4 transistors in one of the two H-Bridges used to drive the actuator motor are blown. This failure then blew a low-side drive transistor and cooked a resistor. (TR7,8,9,10, TR16 and R43 on my reverse engineer'd schematic).

All suspect components now replaced. When I get home I shall see if the thing works.

Andy

 

[underwurlde]

Control board FIXED. Hence boiler now WORKING.

Cancel my search for a replacement!

Andy

 

[sooey]

Well done mate, your knowledge of electronics is wonderful.

 

[Agile]

Good, so PCB now fixed.

But what about all that dirt in the div motor?

Tony

 

[underwurlde]

The old diverter valve was removed & replaced with an *ahem* eBay purchased one.

Andy

 

[Agile]

ood.

But you need to prevent further dirt entering the boiler!

Many would fit a magnetic filter. But I prefer a gauze filter as it keeps out non magnetic parts as well.

WE would normally say power flushing but that's only as good as the person doing it and the chemicals he uses.

The boiler installer is meant to flush the system and ensure the system is clean before the boiler is fitted.

Tony