"Longmansteve" wrote in message
ups.com...
Hi Everyone

I am currently having issues with this boiler. The boiler works
perfectly with the central heating however when using the hot taps in
the house the water that comes out is not fully heated and the
temperature varies from hot to luke warm.

The boiler has been reset and the taps turned at different rates to see
if the flow has any affect - it doesn't.

I am assuming that a thermostat or temperature gauge has gone. Is this
a common problem? Is the solution simple to implement.

Many thanks


Depends, I was surprised to find my Vaillant didn't heat the water to the
demanded temperature, it simply heated it up by X Celsius, depending on how
far you turned the dial. There are several temperature sense thermistors,
but the one in the DHW loop only senses an overheat condition ( 65C ) to
prevent scalding.

If your boiler works the same way (?) the thermistor would have to fail in
such a way as to make the boiler think that luke warm water was an
overheat....

Thermistors are easy to test, there are standard versions, often 2000 Ohms
at 25C is a typical value. I think you ought to consider other possibilities
for your symptoms though. The diverter valve may not work properly on the
DHW side so allowing only a little heat through to the DHW heat exchanger
for instance.

Have you a boiler manual? Have you a voltmeter? Do your CH pipes get hot
when you turn the HW on? Try that test when the CH is off so you can easily
feel if hot water is entering the CH system when it shouldn't be.

Andy.