Vaillant VCW-sine 18 - flow switch/waxstat possible problem?

[Brian R]

Hello,
I am new to this forum and I'm hoping for some help to keep my old faithful Vaillant VCW-sine 18 T3WFH combi boiler working.
It was installed in 1986 and has been an excellent boiler.
I have just replaced diaphragms in the differential valve and the 'water section' which has cured a failure to fire up consistently.
However, I have noticed now that with the central-heating switched off, the 'go' heating pipe close to the boiler is getting hot and the thermometer reading is increasing from ambient when domestic hot water is being supplied (the thermometer should only show the C-H water temperature.)
From previous experience, this suggests that the thermostatic element (waxstat) in the flow switch (diverter valve) is getting sluggish, or may be failing, so I have stripped and cleaned the flowswitch - but the C-H pipes are still warming up. The microswitch above the flow switch has been adjusted correctly in line with the service booklet.

The waxstat body is marked "BTT 7.020.50.299F"

I would appreciate help, if anyone knows a stockist of the waxstat (or an equivalent version), or failing that, the complete flow switch itself, but I suspect it will be like looking for hen's teeth.

Living in hope,

Regards.



Read more: https://www.diynot.com/diy/conversa...e-18-flow-switch-waxstat.36413/#ixzz72CIw8roT

 

[ianmcd]

you wont be able to buy one, your only hope is that someone reading this might have old stock, have you tried e-bay ? sometimes get them on there, very easy to change if you can get a hold of one , good luck, if you ask @ScottishGasMan he might be able to ask for you, he is a trainer with Vaillant and meets lots of their lads

 

[Brian R]

Thanks Ian,
I'll give that a try.

Brian

 

[DP]

The thermometer indicates primary temperature. The sensing tip is located in a pocket on the flow pipe

The reason why the boiler will not see hot water demand is essential because the spindle does not operate one of the microswitches

I am almost certain you can get the complete diverter assembly, van capsule is no longer available

Took out a sine 18 couple of weeks ago for that very issue

 

[Brian R]

Well, I tried to contact @ScottishGasMan as Ian suggested, but failed - apparently I am not allowed to contact him.
So, if John Cassells reads this I should appreciate any pointers he can offer to help me locate a waxstat or flow switch (diverter valve). I was also wondering what the spares situ is like on the German market?

 

[ianmcd]

as you will see his contact details are in blue, so he will be notified that I tagged him, he will get back to you , Im sure, he is a good lad and will help you if he can

 

[Brian R]

Ian, thanks once again.
I'm new to Twitter so at the bottom of the learning curve - but we'll get there I'm sure.

 

[Palingenesis]

I have a Vaillant Boiler VCW Sine 18 20-1 25-1 T3W
It's wax stat no longer opens fully. This causes it to overheat as the water no longer able to flow fast enough through that part of the system.
It also, no longer moves the rod to flip the switch to tell the controller that it is hot enough.
I have found no place to purchase a replacement, I have looked hi and low, with no joy.
If someone know where to get one please let me know.
I have had to come up with an other solution to extend the live of my poor boiler.
It is a simple fix. Not the correct way, but with no other option, it's the only one, and my boiler is still alive. (over 35 years old I think)
It cost £2.00 to do.
If anyone has the exact same problem I can give details.

 

[Brian R]

Hello Palingenesis,

I have not heard from anyone else about my original post, so am interested in your fix and would appreciate details.
I would like to keep it going for a while longer and wondered if an external 3-port motorised valve could be used to switch between domestic hot water and central heating?

Regards

 

[Palingenesis]

Hi Brian,
I came across your post while searching for a fix to my problem.
It all works for about 20 minutes, when the central heating is on it overheats, the the overheat protection cuts in and isolates the electrics shutting the system down.
When using the domestic hot water, washing in sink is OK, but filling a bath or taking a shower, will overheat the system.
Basically if it is on for more than 20 minutes, it over heats.

So my thought was to shut of the gas heater before it reached the emergency shut off temperature.
My simple answer was to get a thermal switch that turns off the gas when it gets to a certain temperature.
Thermal switch
I experimented with several values and settled with 75 degree C.
I made a metal clip that would hold it against the pipe above the thermal resister. (to the back on the left viewed from front).
Wrapped it in tinfoil to transfer heat more efficiently.
On the front of the heating unit there is a large solenoid, it has two terminal.
Disconnect the wire on the left.
Connect the two wires from the thermal switch to the solenoid, one to the wire removed, one to the left terminal on the solenoid.

When the thermal switch reaches its temperature it brakes contact to the solenoid.
When the thermal switch drops 20 degrees below its value it reconnects the solenoid.

If you want photos let me know.

Stay safe.
Tim

 

[DP]

(the thermometer should only show the C-H water temperature.)

Look again, that is primary flow that heats the water so thermometer will be active for both heating and hot water, I am almost certain but last Sine 18 I saw was about a year ago

 

[DP]

Another thing to check. Are the two microswitches under the aluminium cover operated. I suspect that should be the case. As said in my previous post, has been a while since I looked at the Sine 18

https://www.acwilgar.co.uk/Boiler-Manual-PDF/Vaillant/VCW Sine 18 20-1 25-1 T3W.pdf

Use page 46 to fault find the issue.

 

[Palingenesis]

Another thing to check. Are the two microswitches under the aluminium cover operated. I suspect that should be the case. As said in my previous post, has been a while since I looked at the Sine 18

https://www.acwilgar.co.uk/Boiler-Manual-PDF/Vaillant/VCW Sine 18 20-1 25-1 T3W.pdf

Use page 46 to fault find the issue.

As I say in my original post:
"It also, no longer moves the rod to flip the switch to tell the controller that it is hot enough."
The rod is moved by the wax stat.
Switch being the two under the cover.

Read more: https://www.diynot.com/diy/threads/...axstat-possible-problem.575394/#ixzz7IKsRucxa

 

[Brian R]

Thanks DP,
I'll check the switch operation again.

 

[Agile]

I note that Adlink is advertising NOS 14-106 for £120

Was looking up price to charge for one of mine for a client.