Vaillant TurboxMax Plus - Hot Water Problem

[Stuart13]

I have a turbo max plus boiler that his giving problems with hot water flow. The water gets hot but than after a minute goes cold for about 20 seconds, then it gets warm again. When looking at the temperature gauge of the boiler you can see that when the water is switched on it goes up to about 70 degrees, then the boiler switches off until it cools down to about 50 degrees, then it fires back up again to about 70 degrees and the cycle goes on. I changed the thermistor on the hot water and this cured the problem for about 2 weeks, but it has now returned.
Any ideas please?
Kind regards
Stuart

 

[Agile]

It would usually be a blocked secondary heat exchanger.

Odd that you thought replacing the sensor cured the problem for two weeks.

But sensors get coated with oxides and that alters the thermal time constant.

Boilers are complex devices and many aspects interact with each other and many repairs are not just a simple single part to be replaced as most homeowners expect.

Tony