Vaillant Sine 18 no CH

[Tintin007]

I have a Vaillant Sine 18 which has worked flawlessly for more than 18 years. I was in hospital for a week and when I came home I had HW but no CH. When I flicked the programmer the main burner came on for 30 secs or so then went back to pilot.
I checked the flowswitch (diverter valve) at the back of the combi and it was really hot at the top and cold at the bottom. I have taken the valve out and removed the wax capsule (and a lot of gunge in the housing). I boiled up the wax capsule and the pin in the middle moves about 6 or 7 mm upwards.

Thinking that means it was actually working I rebuilt the flowswitch and refilled the system and lit the pilot.....

As soon as I take my finger off the green button the boiler starts the pump and I can hear water flowing through the system. Turning on a hot tap or switching to CH does not light the main burner !

Any suggestions ? I have tried pressing the red button to kill the pilot and I can hear a click after about 20 secs or so. Have also pressed the overheat black button but it is very soft and not convinced it is doing anything....

 

[Agile]

Quite enterprising of you to open up the diverter and test the element.

But the top part is probably jammed and not returning to the CH position.

Also the pin on the wax element does need to push hard and testing out of the unit is not the same as testing with a resistance against it.

Spares are getting very difficult to find now.

I think I still have about six water diaphragms and three wax elements for my own customers!

Tony

 

[Tintin007]

Thanks for the quick reply - I was worried I had now got a different fault.

The valve that the pin pushes against is pretty strong so all I have done is show up the fault at the top end of the valve. When I had HW if I pushed the spindle (at the back of the flowvalve) down the main burner would come on. Now it doesn't....

So the fact that the pump runs all the time still points to a faulty flowswitch. I don't have a problem buying a replacement flowswitch if it will give be a working boiler (both HW and CH). eBay seems to be the only place I can find for a reconditioned valve at £150 exchange.

 

[Agile]

Is the shaft at the top moving for the full travel which from memory is about 8 mm ?

If its moving correctly then you did not need to open the bottom part!

And if so then the problem may be with the switches or their adjustment.

They need careful adjustment and the whole design of the switch assembly is not a very good one in my opinion.

Tony

 

[Tintin007]

It is only moving about 4mm or so - I will check if the microswitch is working correctly. I can press it down the 4mm and the spring looks compressed - ie it cannot move down anymore. Does that spindle move downwards against the spring when boiler is operating correctly ?

 

[Tintin007]

Right hand switch (red and brown wires) was not adjusted properly - when in the rest position it was making contact. I have adjusted the nyloc nut to allow the spindle to move higher and now the switch is open (no contact) when at rest. Boiler is now quiet (normal) when pilot lit. Boiler still not firing on main burner. When I run a hot tap the boiler runs but main burner does not light. When CH is flicked again the boiler springs to life and pump runs but no main burner.......

I am on crutches (fractured hip) so everything seems to take 3 or 4 times longer than previously !!

 

[Agile]

Hoping I am getting this right!

When there is no DHW flow then the conduction through the valve allows the bottom section to get hot and the wax stat expands and the pin moves up and puts the valve into the CH position.

When there is a DHW flow the wax stat cools and retracts. The top section contains a spring which pushes the inside parts down.

As I said the movement from memory is about 8 mm. Its probably either a sticking top section or a lazy wax stat.

Did you take the upper section apart and clean it?

Tony

 

[Agile]

Hoping I am getting this right!

When there is no DHW flow then the conduction through the valve allows the bottom section to get hot and the wax stat expands and the pin moves up and puts the valve into the CH position.

When there is a DHW flow the wax stat cools and retracts. The top section contains a spring which pushes the inside parts down.

As I said the movement from memory is about 8 mm. Its probably either a sticking top section or a lazy wax stat.

Did you take the upper section apart and clean it?

Tony

 

[Tintin007]

Sounds like I need to take the valve off again again and have a look at the top section and see how munge there is in there....

I did take off the section above the wax capsule housing but that did not really help !

The left hand microswitch looks strange since the lever/bracket that actuates the microswitch is a long way from the little black button.

Hopefully taking the top off will give me some clue as to how the whole thing works. Will do first thing tomorrow morning.

Many thanks for your help so far.

 

[Bunnyman]

A good effort tony, O/P, when the valve is in rest, ie hw position the right hand switch should be made, I think from reading ur post u have adjusted it to be open?, the left hand switch should be broken. When the wax stat is heated for c/h the valve lifts, breaks the R/h switch , going over to the fixed potentiometer, an keeps rising until the left switch is made, then this switches the variable potentiometer adjusted by the White thermostat knob..
Sounds like either the top assembly is seized or wax stats knackered

 

[Agile]

Sounds like either the top assembly is seized or wax stats knackered

Great minds think alike!

 

[Tintin007]

Removed top half of valve - seems ok, nothing jammed or stuck.

Wax capsule is the culprit - it does not move far enough or strongly enough to operate the valve in the main body. Will pack it up and send it off for a reconditioned unit which should be here in a couple of days.

Hopefully that will fix it for another 20 years or so !

 

[Agile]

Does anyone know how these can get "reconditioned"?

I am sure that they must be very similar to some used somewhere else like in TRV heads etc.

If only you knew what!

Tony

 

[Tintin007]

Still waiting on the replacement valve (UPS had problems picking up my old one) so ended up removing what Vaillant describe as a heat-exchanger. The tank that sits in front of the flowswitch.

Flushed it through with plenty of water. There was a drainplug in the middle of the bottom but there is also something similar on the top.

Is there anything I need to do to vent this heat-exchanger when I refill the system or does the vent at the top of the boiler do everything ?

 

[Bunnyman]

The plug on the top of the dhw ht exch, is where u vent it from