Vaillant diverter valve failure
The diverter valve on Vaillant combi boilers is a bit of a weak point. The design of the diverter on the current ecoTEC models is essentially the same one they started out with on the TURBOmax and ecoMAX models. This design is based on a pin which moves in and out moving a small piston via a little motor. There is a little O ring seal around the pin which tends to leak. The piston diverts the flow of hot water from the primary heat exchanger either down the flow pipe for heating, or around the plate heat exchanger for hot water. Combi boilers of this type are what you refer to as having an indirect design.
Unfortunately the diverter valve leak issue is quite a big problem with these boilers and with diverter valves based on this design in general. When a customer tells me their Vaillant ecoTEC combi boiler is leaking slightly and loosing pressure it is generally from one of two places – the diverter valve or the auto air vent on top of the pump(sometimes both). Apart from leaking, the diverter valves on the ecoTEC range are generally robust and don’t tend to suffer from most of the other issues associated with diverter valve failure.
Unfortunately diverter valves are a weak point on a lot of boilers, not just Vaillant’s. Most combi boilers on the market today are based on the indirect design which means most of them have diverter valves. Like Vaillant’s, most of them are based on the pin design which are prone to leaking. Intergas is an example of one manufacturer that uses the direct design which does not need a diverter valve. Other manufacturers including the likes of Worcester have dabbled with the direct design in the past, but almost all of them rely upon a diverter valve of some sort currently.
In my opinion, the Worcester Greenstar range of combi boilers has one of the best diverter valve designs I have seen. These are based on a paddle operated by a motor. They work really well and don’t leak very often. Sometimes the motor fails.
Advice: Often problems with combi boilers can be attributed to the diverter valve – especially hot water problems.
All of the components I have mentioned (diverter valve, motor) can be tested in various ways to determine what needs replacing to fix a certain problem. No guesswork should be necessary for any “engineer” to replace a diverter valve to fix a particular problem. Replacing parts on boilers based on guesswork is almost always an expensive endeavour for someone.
As an end user your only option is to call someone competent, qualified and Gas Safe registered to fix problems with your boiler.
It is important to note that this is NOT intended to help other engineers and it is most definitely NOT intended as a DIY self help guide for homeowners trying to fix their own boilers.
If you are an engineer seeking information on how to fix this problem and this has been helpful in some way then thats great. However this page is for information purposes only and cannot be relied upon by someone attempting to carry out any repair – regardless of their qualifications. Read my disclaimer before attempting to use any information on this website.
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