Vaillant VCW242 diverter valve question

[Lacy]

Hi folks,

I have joined the forum after a google search showed there to be some knowledgeable folks here regarding these old Vaillant boilers!

I have had the boiler for over 20 years now and it has been a model of reliability really. The only things I have had to do to it are replace the DHW heat exchanger, the auto vent valve and the fan (twice!)

Anyway, my current problem revolves around the diverter valve. The DHW had been a bit temperamental over the past week or so resulting in it failing altogether tonight.....so I came home from work at 1o'clock in the morning with my wife begging me to sort it out so she could have a shower!

On checking the diverter valve I could see that the arm wasn't coming out far enough to release the lower micro switch. I adjusted the rod a little (2 full turns) so it now operates and still opens well after the top one and closes well before the top one does so there is still a good overlap in the operation of the two switches.

My question relates to how quickly should the diverter valve operate? With the heating on, opening a hot tap sees the valve taking about 10 seconds or so to open enough to clear the bottom switch. Shutting off the tap it then takes a good 3 1/2 minutes or so for the arm to move back enough to close the top switch and turn the heating back on. Does that sound about right or am I looking at springing for a new diverter valve.....or could the problem be elsewhere?

Many thanks for your time.

Lacy

 

[Gasguru]

Diverter should react instantly and only take a few seconds to move either way.

Start with the following...

Blockage in the control tube to diverter coupling (sometimes there's a restrictor/valve arrangement...if so bin it)

DHW diapgragm worn

DHW gland worn

Incorrect adjustment of the water valve/cam/microswitch

Servo valve (on top of the wwater section)

Blockage in the control tubes from the servo valve

Weak pump

Trapped air...is the auto air vent working ok

etc

etc

 

[Lacy]

Thanks Gasguru....a few bits to look at!

 

[Lacy]

A quick update.

Although I had got it all working, late on Christmas Eve, the central heating packed up. Checking the diverter valve showed that it would now not move away from the DHW position. I was reluctant to tear into it until today as we still had hot water and if I started to dismantle on a bank holiday and found I needed a part to get it working I could well end up losing the DHW as well!

Today, I started with the control tubes to the diverter. They were clear but at least with the tubes off, the diverter could be moved manually and a healthy spurt of water emanated from the diverter so I was fairly confident that it was probably OK. Also, when it was stuck in the DHW position, any amount of effort to push the operating arm proved fruitless so I was fairly sure the diaphragm in the diverter valve was OK. Also the cam and micro switch on the back of the servo valve appeared to be working fine so I was fairly happy that the problem was either the servo valve or the control tubes.

After checking the servo to diverter tubes I checked the other control tubes to the servo valve. The last one I checked (isn't it always the way!) was blocked where it entered the servo. I think this is the one that provides the 'feed' to the servo from the top of the pump. It was a bit of a bugger to remove and refit but The operating arm on the diverter now comes out further than it did before (allowing me to reset the bottom switch to its original position) and both hot water and DHW seem to be working reliably now. I have cycled the hot water on and off and, although it still takes maybe 10 seconds or so for the diverter to return from DHW to heating, that's a damn sight better that 3 1/2 minutes or not at all!

Anyway, it's working now. I also have a much greater understanding of how it works so, should it fail in the future I will have a better idea of where I'm looking.

Thanks a million Gasguru. You have saved me a fortune in calling out an engineer...plus I get the satisfaction of sorting it out myself!

 

[Agile]

You are also lucky because there are few engineers who want to bother themselves with older boilers like that.

Probably also only a very small number who understand very well how they work!

Tony

 

[Lacy]

Indeed...which is sad really...I know these old boilers may not be the most efficient things in the world but they are built like tanks and, with most parts still available, there really is no reason why they should not be repaired fairly cheaply rather than written off. I fully expect that if I called an engineer in I would get a sharp intake of breath followed by a quote for 2.5k-3k for a new boiler!

I'm sure the day will come when it needs to be replaced...but that day ain't today!

For the same reason, I drive a Landrover and an old Triumph 2000.....and ride an old Buell...I don't need to plug them in to anything to fix them!

 

[Agile]

To be honest they were rather over engineered.

They are the only model I can think of which has a three position diverter valve.

In many ways the older Sine 18 w, although unusual in its design, was more simple!

Tony

 

[Bunnyman]

A very reliable bit of kit the vcws c u Saturday?

 

[Agile]

Yes!

 

[Agile]

For the same reason, I drive a Landrover and an old Triumph 2000.....and ride an old Buell...I don't need to plug them in to anything to fix them!

Even the Landrovers have been downgraded! They no longer have a starting handle!

If the batts flat you have to push them!

Not just you, but several of you!

 

[Lacy]

Just a quick update for those still interested!

The boiler stopped working again. This time, the diverter valve was resolutely staying in the centre position. It wouldn't move either way. Checked all the little servo pipes again, still nice and clear so I reckoned it must be the servo valve. Bingo!...Changed the valve, now switching from heating to hot water as swift as a swift thing......not too bad to change, a bit fiddly but perfectly doable if you're methodical.

Opened up the old servo valve to take a look...full of horrid black scale that was obviously blocking the ports up......time to fit one of those fancy magnetic filters I reckon to try and get some of the crap out of the system. I suppose a power flush might be a good idea too.....what do folks reckon?

 

[mickyg]

wouldnt bother with a powerflush unless the rads have cold arcs across the bottom. Magnetic filter would do no harm, always a good investment.

 

[Lacy]

Thanks mickyg. I realise I'm in the realms of damage limitation here but I reckon one of those filters, as you say, can do no harm and might help remove some of the crap out of the system. Seeing just how small those ports are in the inside of the servo valve makes me realise just how clean the system needs to be and, well, every little helps!