Vaillant VCW242EH Luke warm DHW

[topfridgeman]

Hello Guys,

I've got a problem with a VCW242EH Vaillant boiler. It runs the radiators ok, but just provides luke warm DHW. I've checked the pump and diverter, which look fine. When the DHW is running flat out the water on the boiler side gets very hot, but the DHW doesn't seem to be picking up any heat from the boiler. I'm fairly happy that it's the heat ex playing up, but I'm unable to check the DHW sensor. Has anybody had a problem with the sensors, or a resistance chart etc to check the sensor? Also has anyone got a number for the heat ex so I can see which ones will fit.

Thanks, in advance, Col.

 

[Andygasman2010]

Hi. Sounds like you're right to me, the plate heat ex will be blocked. I've never had one of those sensors fail they're very good so i've got no testing info. All i do is pull the wire off it, this will keep the burner on high gas. If you then get kettling and better hot water you know 99% that it's the heat ex. This is the one for your boiler.

https://www.abcotuk.co.uk/Product.asp?ProductId=P215&Catid=C2

You could just strip it down and soak it in a strong acid cleaner like spirits of salts (HCL) i've even used vinegar before, works suprisingly well!

 

[Bunnyman]

Hi mate the domestic ht exch on the vcw s r on the left hand side if it's the earlier black plastic one u can't descale it u have to replace with a steel one with the pipe adaptor kit 065034 if it has the metal one u can descale if ur careful. It won't be the sensor on these they don't go wrong

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[Andygasman2010]

Hi mate the domestic ht exch on the vcw s r on the left hand side if it's the earlier black plastic one u can't descale it u have to replace with a steel one with the pipe adaptor kit 065034 if it has the metal one u can descale if ur careful. It won't be the sensor on these they don't go wrong

Untitled

• Bunnyman
• 26 Mar 2010
• 499

Cheers! Forgot about it possibly having a black plastic one

 

[topfridgeman]

Thanks guys.
The boiler has the upgrade stainless heat ex fitted. I tried taking the wire off the sensor, and it made no difference. I have some strong acid cleaner, so I'll try that as a new heat ex is about £90.

Col.

 

[Andygasman2010]

Pulling the wire off made no difference... That's curious. If it's staying on high gas and you're still getting luke warm water, maybe the diverter is passing...? Or maybe it osn't actually on high gas and there's some kind of modulation/gas pressure problem. I'd be a little worried it's not the heat exchanger now.

 

[Agile]

Measure the resistance of the sensor with its wire disconnected.

I think its about 1.3 K with the boiler at room temp ( 20° ).

But can be several other causes some of which are gas related and would need a registered engineer.

Tony

 

[Andygasman2010]

The sensor is within the combustion chamber anyway so it's already a bit of a naughty one!

Wire off should be high gas, earth the wire out should cut the burner off. I've never had to take it further that, never had one of them fail before.

 

[Agile]

Oops, cancel that suggestion then.

I was thinking of the earlier Sine 18 and the later Turbomax!

Anything inside the combustion chamber needs an RGI to open it.

BUT

It can be safely be measured at the plug which connects it to the PCB after the plug has been removed from the PCB.

Tony

 

[Bunnyman]

tony all turbomax ntcs r inside combustion chamber dont both measuring them in 25yrs of mendind vaillants only had 2 fail!!it wont be that..

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[Bunnyman]

measure flow rate at tap it should be 7.6 l/m or there abouts.if you got more than that suspect busted flow regulator on the front of the water valve or maybe u got a duff shower somewhere allowin cold water to cross over?put hot tap on full an put your hand on the hot outlet pipe from boiler if its hot its prob a duff shower mixer if its only luke warm its prob duff flow regulator

Untitled

• Bunnyman
• 26 Mar 2010
• 499