Faulty Vaillant VCW GB 242 EH boiler

[prthomas]

hi, i have a Vaillant VCW GB 242 EH boiler.

we are getting hot water for about 30 seconds, then it starts to go cold. eg: the water in the shower is fine then it goes tepid at best after 30sec, even when the hot is on full.

i have been told that this problem is the diverter value, is this correct?

if so, does anyone know what is the rough cost and best option to rectify the problem?

any help would be much appreciated

 

[dfaz]

hi Im presuming you have the same problems with all your taps not just your shower but do check your shower is not passing and blending your hw temperature.first turn off the right hand return service valve to your boiler if you then have hot water you may have a diverter problem,this is unusual on this model I have only changed 2or three in 21 years .it is more likely you have an issue with gas pressure the incoming water temperature is only about 4 degrees at the moment so the boiler has alot to do,check the gas burner pressures the should be 1.5 min and aprox 6.5-7 ON MAX the book says 5 but trust me they struggle in winter otherwise if that is ok then i suspect your domestic hot water heat exchanger is not tranfering heat as it should,this would allow your boiler to run at higher temperatures and cut out occasionaly then cut back in as it cools the only option then is to replace the heat exchanger,you may have the old black heat exchanger located on the left hand side or if it has been changed or 1995 onwards would have the later plate heat exchanger hope the above helps
Dave

 

[gasright]

hi Im presuming you have the same problems with all your taps not just your shower but do check your shower is not passing and blending your hw temperature.first turn off the right hand return service valve to your boiler if you then have hot water you may have a diverter problem,this is unusual on this model I have only changed 2or three in 21 years .it is more likely you have an issue with gas pressure the incoming water temperature is only about 4 degrees at the moment so the boiler has alot to do,check the gas burner pressures the should be 1.5 min and aprox 6.5-7 ON MAX the book says 5 but trust me they struggle in winter otherwise if that is ok then i suspect your domestic hot water heat exchanger is not tranfering heat as it should,this would allow your boiler to run at higher temperatures and cut out occasionaly then cut back in as it cools the only option then is to replace the heat exchanger,you may have the old black heat exchanger located on the left hand side or if it has been changed or 1995 onwards would have the later plate heat exchanger hope the above helps
Dave

So let me get this right, your asking the original poster to check BP readings.

 

[dfaz]

OOps so used to advising other installers wasnt thinking

 

[prthomas]

thanks dave for your reply

i turned off the return service valve, no water. checked pressure and both fine.
the problem has mainly been in the bathroom... shower and basin. kitchen has been ok-ish.
there is a small leak coming from a small copper pipe that goes into/out of a small diaphragm that obviously has been leaking for a while with the build up of corrosion, see below picture.
would this have anything to do with the hw problem other than a doggy heat exchanger?

/Users/paulrthomas/Desktop/pict01.jpg

 

[prthomas]

Untitled

• prthomas
• 20 Feb 2010
• 1

 

[Agile]

The leak itself would not affect the performance but if its been refilled so many times to compensate for the leak then the system is probably dirty and that could be pointing to a blocked secondary heat exchanger.

Everyone would say that any leak should be fixed as soon as you become aware of it.

Tony

 

[dfaz]

I agree, constant toping up causes corosion within your heating system this then accumulates in the main and especially the secondary hot water heat exchanger.the servo valve has a red microswitch on the back the switch should make fully when you run the tap,you will need a new servo valve and retaining clip befrore you attempt anything on the leak ,it comes with new seals.if you still have the old black heat exchanger you will need a kit which has new pipework to convert it to the new heat exchanger,i should know the part no but heads not with it today ill find it let you know.(part no 065034)as for the kitchen being hotter kitchen taps tend to be more restrictive on flow the water passes through the boiler slower and picks up more heat,just how fast is the water flowing through the taps a 24kw boiler will only provide 9-10 litres p/min if its gushing out of the tap the boiler wont cope.

 

[oily66]

I'm watching this with intrest as my boiler of the same make is doing a similar thing ie hot water for the very shortest of time then cold at all taps, I too have had to constantley top up the boiler lately as it has been blowing off I know that i have to drain it down then top up the expansion vessel. But this has nothing to do with how the DHW is affected. Can you let me know how you get on with clearing the heat exchanger. Mine has the new ish type metal one fitted approx 3year ago.

 

[dfaz]

make sure your heating is switched off so you know your hot water switch is activating and staying on, the diverter valve will move across to the right.
if the temperature guage is working on the front of the boiler and you have a blocked heat exchanger you will see a sharp rise in temperature 80 + degrees and cool water at the taps with the flow rate filling a builders bucket in aprox2 mins.if you slow the tap down you may see the gas rate reduce and still very little hot water temp rise.If you can get someone who is gas reg if you arnt allready ,you would see the gas regulate down to as little as 1.5 millibar this weather the boiler should be working hard and gas pressures should be6.5 -7 millibar.

 

[dfaz]

if you have a new plate type heat exchanger they are difficult to clear even with a powerflushing machine,and probably better to replace it

 

[Homesafe]

where abouts in lancs are you DFaz?

 

[dfaz]

In sunny Morecambe

 

[Homesafe]

sounds good, went ther when I was younger.

 

[Agile]

I went there a while ago too. We had a VHF transmittter there.

Possibly also a DF facility.

Tony