Replacing heat exchanger in Vaillant VCW GB 242EH Combi

[fastbike]

Hi Folks,

The plastic-housed secondary heat exchanger leaks so I have got a the recommended replacement 06-5034 which is a more modern metal plate type.

It's supplied with a new set of pipework to allow it to fit, but I've heard that some adjustment of the control circuit (component removal?) and a modification to the diverter valve (disk?) is required.

Unfortunately I got no instructions or information about this - can anyone assist ?

Thanks,

- Steve

 

[pipe]

isolate boiler from electrical supply.Remove the four screws holding in the control box.Slide control box forward to access electronic circuit board.Identify bridge wire w18 on board, carefully cut wire to break link.Slide control box back & replace screws.As for the disc you will have to remove diverter valve,If valve is oldish, may as well fit a new one.Hope this helps.

 

[fastbike]

Gosh, that's quick ! Thanks !

Do you know what these mods actually do ?
I'm not sure what "disc" is being referred to; I've certainly not got any spare discs with the kit.

Really just trying to establish whether this aspect is critical

Thanks again

- Steve

 

[chrishutt]

Your replacement secondary heat exchanger should contain a set of instructions as well as a replacement disc for the diverter valve. Did you get a Vaillant spare or a much cheaper unofficial version (£40)?

If your boiler is a hybrid model, you need to cut a link (W18) on the electronic board. A hybrid model will have a plastic variable potentiometer knob (temperature dial) spindle, whereas the non-hybrid will have a brass variable potentiometer knob spindle.

You are also meant to replace the disc in the diverter valve. The original disc has by-pass grooves that allow water to pass through the secondary heat exchanger when in CH mode to maintain a store of hot water. The new disc does not allow water to by-pass. If water continued to by-pass, the new heat exchanger would be overheated and might scale up in a short time, depending on hardness of water.

Dismantling and reinstalling the diverter valve is quite a difficult and complicated job (1 hour if you know what you're doing), and it is likely that many engineers don't bother with this.

 

[fastbike]

Wow, thanks Chris. That's exactly the sort of info I'm looking for.

The kit I bought cost around £80, made by Zilmet so I assume that it's non-original, but looks decent quality and it did come withe decent set of 4 new pipes, replacement washers etc.

I've just checked - my controller has a brass pot spindle so I assume it's a non-hybrid model. Does this mean I shouldn't need to cut the wire link ?

I understand your point about the "store of hot water" but my boiler certainly doesn't seem to make much effort at that. As a test, If I draw a trickle of water from the hot tap - insufficient to switch the diverter valve - the inlet to the secondary heat exchanger is barely warm, and the "hot water" is fairly cool too. My conclusion is that it's not allowing much water to bypass.

I'm tempted to leave the diverter alone, safe in the knowledge that I can remove and descale the heat exchanger if it does start to scale up.

- Steve

 

[fastbike]

- oh and by the way, I did't get any instructions whatsoever, or the "replacement disc"

- Steve

 

[chrishutt]

Well, you can forget about cutting links on the electronic board, and I think you are being sensible in steering clear of tackling diverter valve. Depending on where you live, it might be an idea to fit a scale inhibitor to the cold water flow.

 

[fastbike]

Thanks, Chris.

Yes, I've already got a "scale inhibitor".

Despite being a professional engineer, I'm convinced that it works exclusively by magic.

It's just a few turns of wire around the incoming water pipe, with a few magic electric waveforms passed through them. Nevertheless, the existing heat exchanger is still giving fairly good flow even in my hard water area (Portsmouth), so I suspect that the magic is working...

- Steve

 

[fastbike]

Oh, and that is after approx. 18 years of use, by the way !

 

[chrishutt]

That's interesting to hear. I've always wondered about these electronic scale inhibitors. I understand that they work by modifying the surface texture of the scale crystals so that they don't stick to other surfaces so easily. As far as I know no one has ever carried out independent tests to determine whether they work - a rather sad sign of the times I think.

 

[fastbike]

Yep, I assumed that those scale inhibitors were complete nonsence, although as mine was free (it's a prototype - a friend designed the electronics), I assumed that it wouldn't do any harm.

Now, I'm rather more convinced. When I completely replumbed the kitchen recently, there was no scale to speak of in the old pipes at all.

Thanks again for your excellent advice.

- Steve

 

[Agile]

The electronic and the magnetic scale conditioners operate by modifying the molecules of hardness disolved in the water.

The magnetic ones do seem to have a useful effect. The current in the electronic ones is so weak that the resulting magnetic field will be so weak that I am very dubious if they have any effect at all.

I have a 35 y.o. CH boiler and a standard Grunfoss 15-60 pump used to heat DIRECT water for a launderette. Its never been descaled and still seems fine. I have a magnetic treatment formed from a ceramic magnet from a large loudspeaker and pole pieces to apply it to the 22 mm copper pipe supplying the pump and boiler, a CH502 !

Tony Glazier

 

[ChrisR]

It's always interesting to do a scientific assessment of scale build up in old heat exchangers in hardish water areas. Highly scientific lump hammer may be useful!

 

[chrishutt]

The current in the electronic ones is so weak that the resulting magnetic field will be so weak that I am very dubious if they have any effect at all.

As I understand it,the electronic conditioners due not attempt to operate in the same way as magnetic ones. See tech info at http://www.hydroflow.force9.co.uk/index.htm for details.

 

[Agile]

Well if you understand that ( nonsence ) then how do you explain how an electric field into the inside of a copper pipe.

The other ( nonsence ) is generating an electron flow ( thats a current ) in an "open circuit".

My advice is to stick to the magnetic type!

Tony

PS for anyone who does not know, an electric current always generates a magnetic field around the conductor.