Vaillant luke warm bath tap

[andybd1]

Hi.
My system is a Vaillant Turbo max plus 824E. All is fine untill the bath tap is turned on fully, then the water temp drops to about 28deg. If the tap is turned on half the temp is correct. Not what I needed after Christmas but just getting an idea of what this might cost me.
My trade is auto electricial diagnostics so I wont do more than the basics with this, I have the boiles service manual and looking at the pretty pictures inside I am suspecting a possible diverter valve or heat exchanger issue, but Im hoping Ive overlooked the small reset button I need to press! (well I can hope eh). Oh yes lights on the front are correct and no code are flashing on the display.
Thanks.

 

[HootingOwl]

has the bath tap become cooler recently? or has this been going on for some time?

your boiler is 24kw output and will not be able to heat a large volume of water on demand - especially in winter when the cold water entering the house is much cooler than in summer months.

you need to look in the manual at the flow rate for domestic hot water. and then measure the flow rate at the bath tap using a bucket and a measuring jug. what is the flow rate at full-bore? and what is it at half-bore?


you may find that there is nothing wrong with the boiler.

if the flow rates check out, then look in the FAQ section and gas rate the boiler on hot water mode. post your results here and we can go from there...

 

[andybd1]

Hot water has only been an issue for the last three days. It has been ok for last 5 years so I dont think it is a weather problem. Even with CH off the hot water is the same up stairs and down, increase flow more than 50% on any tap and it runs cool.
Have noticed today that if the hot water demand is left on, after 10 minutes the rad tem starts to get hotter! Diverter valve issue?
Thanks.
Andy.

 

[Iamnuts]

I have the same boiler and periodicaly have your problem too.

The solution for me and a great many others is to remove and clean/descale the dhw heat exchanger, its quite a common fault on those boilers.

Ive seen replacements if you dont want to do that from between 50 quid to 130 quid. fiddly to remove and refit but diy-able

 

[bobw1956]

.
Have noticed today that if the hot water demand is left on, after 10 minutes the rad tem starts to get hotter! Diverter valve issue?
Yes your right it,s the diverter valve

 

[LUNAT]

HI


I would agree with hootingowl.24kw is not big enough for hw and this diferrence can be seen in winter.

 

[andybd1]

No sorry, Im not believing it cant cope with the winter, it has for the last 5 years and as I say even with the heating off the tap temp is the same, Is the fact the heater output pipe gets hotter when the hot water demand is increased a pointer to diverter valve, or could the DHW heat exchanger give these same symptoms?
Andy.

 

[Agile]

Step back and ignore the wrong advice.

This is a clear case of the failed diverter valve as suggested.

You are lucky its worked for so long! Most failed within three years!

Tony

 

[andybd1]

Thanks Agile I had sort of come to this conclussion but at over 140 pounds I needed a push in the correct direction, but erring on the side of caution I had just found a repair kit, number 140352 on flea bay, and pressed the no return button. Thanks will post result.

 

[mickyg]

thats not for your boiler. you need the complete valve. its not possible to repair it.

 

[Agile]

The price for the CORRECT replacement diverter valve should be under £100 !

Try a part number of 252457 !

They are replaced, not repaired!

Looks as if we only have one left in stock!

Tony