Vaillant VCW 242 EH/282 EH, HW OK, CH very intermittent

[Mike13]

Hi,

I recently had to change the DHW heat exchanger and now the heating is very intermittent, it just runs cold, the heating pump is running and warm for long periods, but the radiators stay cold.

Also a question about the kit to change from the plastic to the metal DHW unit, it asks you to cut a link on the circuit board if you have a hybrid board, how do I know by looking at it if it is indeed the hybrid?

And in the kit was a brass disc with a rubber washer on each side, where does that go, as there is nowhere in the DHW diverter valve assembly, as I have opened that up to check.

Mike

PS the unit is of unknown age as it was in the house when we moved in.

The copy of the wiring diagram in the lower cover states

VCW GB242E, 282E 80 65 46 GB 04

 

[DP]

Do a serach. Plenty on the forum to help you get to the root of the problem

 

[Mike13]

well as I was in the middle of a crisis, trying to get the heating working and keep the two little ones warm, that last bit of advice had zero value for me.

It is now sort of functional, but the hot water is now luke warm when the tap is fully open, it flows at real ale temperatures at 11 litres per minute.
Anyone got any advice of what it could be?

In the last year or so the boiler has had a new diaphragm in the hot water diverter, a new heat exchanger and a new bit that screws onto the gas section with 3 screws, I don't know what that is called. I have also cleaned out the diverter valve and changed the insert provided in the heat exchanger kit. The link has been cut on the hybrid PCB.

Mike

 

[Gasguru]

The boiler is only capable of producing around 9 litres/min raised by 35 Centigrade so turn the flow rate down and see if the temperature improves.

Otherwise check the heating flow pipe is not getting hot when in DHW mode; if it does the diverter is letting by.

Next would be to open the tap fully and measure the gas consumption at the meter. Time the test dial for 1 revolution. If no test dial measure the difference in the 3 right hand digits over 2 minutes.

Post results.

 

[Mike13]

Hi Gasguru,

How do I change the flow rate? I will measure the gas consumption shortly. The thing is, just a week or so ago, before I changed the heatexchanger that sprung a bad leak, the hotwater was just fine. the 9 or so litres per min was adequate. I suspect it is an adjustment somewhere in the DHW diverter valve perhaps, but I dont know which bit to adjust?

Mike

 

[DP]

Advise I gave (do a search) would have given you instant insight into what you wanted to know.

While the regulars visit these pages at random, doing a search would have let you get on with problem in hand and restored the heating to keep your family warm!!

 

[ChrisR]

How do I change the flow rate?

Don't open the tap as far.

 

[Mike13]

Advise I gave (do a search) would have given you instant insight into what you wanted to know.

While the regulars visit these pages at random, doing a search would have let you get on with problem in hand and restored the heating to keep your family warm!!

For a part timer to the board like me the search turns up so much irrelevant stuff that it is not a great help, it needs hours and hours of reading to find anything relevant.


I have decided that this is the last Vaillant I will ever own, more trouble than it is worth. I keep having to flush the system every few months to keep it working, it is impossible to find a plumber that understands it, I see no point in having an over-engineered boiler, it is more trouble than it is worth.

 

[Gasguru]

The boiler is only capable of producing around 9 litres/min raised by 35 Centigrade so turn the flow rate down and see if the temperature improves.

Otherwise check the heating flow pipe is not getting hot when in DHW mode; if it does the diverter is letting by.

Next would be to open the tap fully and measure the gas consumption at the meter. Time the test dial for 1 revolution. If no test dial measure the difference in the 3 right hand digits over 2 minutes.

Post results.

So have you turned down the tap to 9 litres/min to see if the water is now sufficiently hot?

No good complaining if you don't carry out simple diagnostic checks.

The water may be flowing at a higher rate with the new plate heat exchanger than with the old plastic heat exchanger. You can always adjust the water flow rate into the boiler with the valve on the water section but it is normally more flexible to adjust at the taps.

I guarantee many CombiCompact VCWs will outlast some of todays recently installed condensing boilers. It may be over-complex/over-engineered but that makes them bullet proof.

Why are you flushing the system eevry few months? - that's the worst thing you can do to any system. Everytime you refill you deposit more scale in the heat exchanger.

 

[Mike13]

Well the heat is fine if you drop the flow, as mentioned I just asked how to set up the max flow to 9 litres per min.
The reason for regular flushing is because it keeps not heating the rads unless it is cleaned out yet again. I said I was unhappy that I had to keep doing it to keep it as a working system.

So what part is it that I adjust to drop the max flow rate? If I try to use the incoming water valve for the heating loop it is too close to totally shut to trust that as an adjustment.

Mike

 

[Gasguru]

So are you saying that at a sensible water flow rate the boiler is working fine then?

I don't understand why you can't use the valve on the water section to limit the flow. Most people use judgement and turn each individule tap to a sensible flowrate. You could install flow limiters into the hot pipework just before the hot taps. Are you on exceptionally high water pressure? If so consider fitting a pressure reducing valve after yours mains stopcock.

Flushing the system on a regular basis is killing the system. Find the cause of the problem. Are you using a quality inhibitor? Perhaps it needs a proper chemical clean, perhaps it's suffering from bacterial growth or some other problem.

When you replaced the heat exchanger did you clean out all the control tubes and the banjo restriction. Have you replaced the servo valve? Did you replace the auto air vent. With the age these boilers are if these simple items are not working 100% you will get heating problems.

 

[Mike13]

The boiler works at normal flow rates, the hot water was working fairly fine before the dhw heat exchanger replacement. I would adjust the valve if I knew where it was, I dont really want to adjust things unless I know what they are, and where I can find them in the boiler.
I use an inhibitor from the local plumbers merchant, I have been trying a different one each time, it doesnt seem to make a lot of difference.

Mike