Vaillant Combi VCW-Sine 18 T3WF H

[Bunnyman]

Just jumpin back in again between u 2 lovebirds lol! Mac u say u can see why it causes the chattering on hot water but can't under stand y it does not on heating, well when this fault has been present for a while and gets worse u will find that when the lhs micr switch makes on the divertor that the variable stat does not come into operation an causes the manual overheat to operate , please let me know the out come of this

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• Bunnyman
• 26 Mar 2010
• 499

 

[Agile]

Well I am lost with this.

Mac says that he has tested the microswitch. I am sure he has properly tested it to measure the resistance of the NO and NC contacts down to less than one ohm.

In that case whats the problem with it?

Tony

 

[The831Bunny]

My god what a complete load of speculation about a very common problem!!! S3 microswitch as it's known (126215) will develop a high resistance between contacts, and when changing over even go open circuit momentarily. This causes the DC Solenoid to reenergise and the process is repeated quickly hence the machine gun effect. The point it occurs is when the weatstone bridge is equalised (primary temp around 80c before wax stat lifts). It also happens when the heating pot temp is achieved as well and as the Bunnyman rightly says leads to OH as the burner sits on low gas till the OH stat trips.

Just change the switch and while you're there dismantle and grease the pin on top of the solenoid (it dries and sticks). Also adjust the pot on the solenoid for a 3 second 'dwell' on low flame for softer ignition.

You can use a MS from Maplins/RS etc, but the NC and NO tags are usually reversed to Vaillants genuine switch, so adjust wiring accordingly.

 

[MacII]

But thats not the ONLY way the pump is activated.

In CH mode the pump normally operates continually and the burner step modulates and if it is then still too hot the gas solenoid is turned off but the pump STAYS on!

Tony

Sorry had to go out last night.....Yes you are correct. I should have mentioned that the configuration on the system has TRV's and clock. No room thermostat.

The VCW has three differnt ways to control the pump depending on external devices and position the Vaillant pump selector link is in. Mine is in position II. So yes you are correct many ways to switch the pump on and off....

I like the explanation of the Sun Dial investigation...I bet your mum and dad had their hands full!

Again many thanks for the help. Going to rumage in the junk box for a microswitch as you suggest...I am sure I have one.

Have very much enjoyed the dialogue.

I'll let you know if the Bunnyman fix works...

All the best

Bill

 

[MacII]

My god what a complete load of speculation about a very common problem!!! S3 microswitch as it's known (126215) will develop a high resistance between contacts, and when changing over even go open circuit momentarily. This causes the DC Solenoid to reenergise and the process is repeated quickly hence the machine gun effect. The point it occurs is when the weatstone bridge is equalised (primary temp around 80c before wax stat lifts). It also happens when the heating pot temp is achieved as well and as the Bunnyman rightly says leads to OH as the burner sits on low gas till the OH stat trips.

Just change the switch and while you're there dismantle and grease the pin on top of the solenoid (it dries and sticks). Also adjust the pot on the solenoid for a 3 second 'dwell' on low flame for softer ignition.

THat is a brilliant explanantion...Top man.

Many thanks

Bill
You can use a MS from Maplins/RS etc, but the NC and NO tags are usually reversed to Vaillants genuine switch, so adjust wiring accordingly.

 

[MacII]

Well I am lost with this.

Mac says that he has tested the microswitch. I am sure he has properly tested it to measure the resistance of the NO and NC contacts down to less than one ohm.

In that case whats the problem with it?

Tony

Tony,

I have to admit to all I only used a continuity tester with audio to check the microswitch contacts. Hindsight is a wonderful thing....I should have checked it more thoroughly using digital Ohm meter......Could kick myself....

All the best

Bill
Bill

 

[DP]

Mac, I am sure your continuity tester will have been adequate for 'GO' or 'NO GO' test.

If anything, digital multimeter would show digital response of what it 'sees'. Fact remains it has very high input resistance, so it can give some reading (even through surface dirt etc) when in fact circuit is open circuit since meter 'looks' at the circuit instead of becoming part of it like moveing coil meters use to do when boys wore shorts and were well behaved. Try takeing a reading of water in a tumbler- resistance with digi meter may be very low but your contuity tester may not agree with what the meter says. While in most instances a multimeter is more than man enough to do the job, there are times when a good old Avo 8 beats it hands down.

If the microswitch is connected to a solid state circuit, a few ohms here or there will make little difference (remember, components have tolerances so precision is not name of the game). A 47kΩ resistor with 10% tolerance can be anything from 42.3kΩ to 51.7kΩ. Capacitors can have much larger tolerance. To make circuits that are very precise is expensive and often needless when it comes to what is found in boilers. Components are not made to fall within a talerance window but are manufactured and then tested and marked for the tolerance band.

If the said microswitch is connected to mechanical gear, it is either a short circuit or open circuit. Dirty contacts will often result in poor performance (anyone remember contacts in car distributers?)

 

[Agile]

Mac, I am disapointed with you!

I never thought that anyone who has gone as far as to see how the opamp works will have not tested the microswitch properly.

Its always essential to MEASURE the actual contact resistance to ensure its below one ohm AND that it repeatably the same low value. I operate these about 10 times at least!

Tell us the NO and NC resistances when you measure them! I expect that will show the fault.

Tony

 

[Bunnyman]

Thanks for that 831bunny! Ur better at the technical explanation than me mine is just experience ! An ur right that is ur old van lol! Mine was still in Lye I think!!

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• Bunnyman
• 26 Mar 2010
• 499

 

[MacII]

Mac, I am disapointed with you!

I never thought that anyone who has gone as far as to see how the opamp works will have not tested the microswitch properly.

Its always essential to MEASURE the actual contact resistance to ensure its below one ohm AND that it repeatably the same low value. I operate these about 10 times at least!

Tell us the NO and NC resistances when you measure them! I expect that will show the fault.

Tony

The final chapter..…..I have been to Maplin and installed a new DC Solenoid micro switch (massive cost of £1.69). You guys are MUSTARD! DHW and CH work perfectly. Better than new..No tapping or machine gun noise.

I have to admit I would not have sorted this problem without the forums knowledge and guidance.

I have rechecked the old micro switch with a digital Ohm meter. The resistance between contacts in activated and non activated state is 0.1 Ohm. I have repeatedly tested it. The worst reading is 0.3 Ohm but it consistently reads 0.1 Ohm. The only clue to its malfunction is a softer than usual click as the contacts change over. The actuation button appears to travel slightly too far before the contacts change. It doesn’t seem as precise as the new Maplin micro switch.

Whilst the contact resistance measures good on full and repeated actuation. I can only conclude that the micro switch contact changeover delay/mechanism is faulty/worn rather than a problem with the contact resistance at full idle or active state. Extremely difficult to spot.

I had previously tested the micro switch in situ with the wires off ( I actuated it by inserting a small electrical screw driver between the pin and button) similar to above it tested good. Had I taken the micro switch off and tested it with the digital tester I would probably have still given it a clean bill of health and started looking elsewhere for the problem (exactly what I did). Goodness knows how much time it would have taken me to solve the tapping problem without you guys.

Special thanks to:

• Agile for the fast reply, great support, comprehensive knowledge and not making me feel too technically inadequate.
• Bunnyman for the fast accurate and professional determination. The man with the green van is OUTSTANDING.
• 831Bunnyman for the brilliant technical operation and fix description. Truly INSPIRING.

Again many thanks for the excellent help. Long live the Vaillant VCW Sine 18T!

Best regards

Bill

 

[The831Bunny]

Thanks for your thanks Bill

It's good to know our knowledge is still coming in handy, guess it will all be unneccersery soon with the declining population of T3W's. Until then....

Glad you got it sorted

 

[Bunnyman]

Thanks mate come back again as the 831 said we don't get chance to mend these much now

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• Bunnyman
• 26 Mar 2010
• 499

 

[Agile]

Mac, thanks for that test.

Its essential to repeatedly test the contact resistance in a way that measures the actual resistance.

I am still interested in the problem with your old one. I love technology and identifying malfunctions. Thats why I am a fan of the TV aircraft crash programs where they carefully analyse what the symptoms were and how the crew reacted.

I suspect that the contacts are opening and staying with neither contact made. Obviously the toggle action should be immediate and well defined. The tension of the curved spring inside has probably weakened. That can be tested by clamping the switch and slowly moving the actuator with a caliper gauge whilst monitoring the contact resistance.

If you can test it and let me know that would be good or alternatively post it to me for me to assess.

Tony Glazier



PS Do you think that I should dry out the Sine 18 in my garden and connect it up to perform more detailed operational checks on it?

I may be removing a fully working one during the summer though.

Probably not because if I am unlikely to see many less common faults when I only go to 2-3 each year. Hardly worth spending too much time when there are Ravenheats there to be fixed.

 

[The831Bunny]

PS Do you think that I should dry out the Sine 18 in my garden and connect it up to perform more detailed operational checks on it?

I may be removing a fully working one during the summer though.

Probably not because if I am unlikely to see many less common faults when I only go to 2-3 each year. Hardly worth spending too much time when there are Ravenheats there to be fixed.

I wonder if a Ravenheap would work if left out in the rain for 10 minutes...

I've dug up my Germany training folder for a few nuggets of info for you Tony.

This is unchecked but straight from my notes (possibly effected by too many 330ml of bier )

S3 microswitch switches negatives. MS 'made' circuit Blue to Brown, 'unmade' Black to Brown.
Brown: Negative
Black: Negative to Pump relay (pump runs in pump position 2 (ll)
Blue: Negative to time delay discharge pot

Now if you're really interested I'll scan the Schematics for you...

 

[DP]

Mac wrote

I have rechecked the old micro switch with a digital Ohm meter. The resistance between contacts in activated and non activated state is 0.1 Ohm.

DP wrote

Fact remains it has very high input resistance, so it can give some reading (even through surface dirt etc) when in fact circuit is open circuit since meter 'looks' at the circuit instead of becoming part of it like moveing coil meters use to do when boys wore shorts and were well behaved.

Need I say anymore?