Vaillant TurboMax hot water supply problem

[kirkle]

I have a TurboMax VUW282E which has given many years of good service, however over the past week it has developed a problem with the DHW supply.

When drawing hot water the boiler starts as normal but then after about 15-20 seconds shuts down and then, after about 7 seconds, starts up again. This happens even when there is full demand for hot water. The water is reaching temperature but then of course, when the boiler shuts off, the temperature slowly drops until the boiler reignites. Which means you get a supply of hot water fluctuating from a good supply of hot water to just warm and back up to normal again.

I have ruled out problems with gas supply, burner, DHW microswitch and the diverter valve. The boiler is running perfectly for the CH reaching temperature, modulating etc.

Setting the hot water temperature control high or low makes no difference. The flow from the hot water taps is fine, we have no thermostatic showers or anything like that.

I have concluded that it must be a problem with the DHW heat exchanger, the overheat thermostat or the water section diaphragm. The boiler is not making any funny noises so I don't think the water on either side of the DHW heat exchanger is getting too hot and boiling.

I have read many threads where it has become and expensive trial and error replacement of components to eventually cure the problem and I want to avoid this scenario if possible. As the boiler is now over 12 years old I suspect that many engineers may not be familiar with this model.

Does anyone have any idea of how I can work out which component may be at fault or give enough information to a plumber so the fault can be quickly discovered and rectified?

Many thanks

 

[Billy Bob Bob]

you need a gsr engineer to avoid random changing of components,probably diverter knackered or plate heat,diverter is my bet

 

[tipintim]

Firstly, what an interesting post to read. You have done your homework on your boiler.
Perhaps you need a new one.

 

[moony]

could narrow it down to 4 or 5 things but then its impossible without being in front of the boiler. And really mate you shouldnt be messing with the inside of a boiler as its against the law.

 

[kirkle]

could narrow it down to 4 or 5 things but then its impossible without being in front of the boiler. And really mate you shouldnt be messing with the inside of a boiler as its against the law.

Hi I haven't been messing around with the inside of my boiler. I have just observed what has been happening and utilising the the installation and service manual that I have endeavoured to reach some conclusions. Whether these are correct or not is another matter. Thanks for your advice.

 

[gasmarc]

has the problem been progressive if so I would go for heat exchanger

 

[Puddle]

As said,first port of call,wipe domestic h/e out and clean,pipe will be hot,just not circulating round boiler quick enough

imho

 

[gasmarc]

i usually beat the crap out of it on a piece of wood and run the mains through it . this has worked all the times with no recalls yet but did try spirit of salts which works a treat also

 

[kirkle]

As said,first port of call,wipe domestic h/e out and clean,pipe will be hot,just not circulating round boiler quick enough

imho

Thanks for this info.

Most replies seem to be treating me as if I should just not bother knowing anything about how the boiler works and just call in the "specialist" There is no way I would touch anything to do gas supply on the boiler or other element I don't understand. I have in the past replaced a faulty DHW microswitch when it was obvious where the fault was. Is this a big deal?

Thanks again