vaillant sine 18 combi boiler - diverter valve

Discussion in 'Plumbers' Talk' started by Chatsworth, Aug 23, 2005.

  1. Chatsworth

    Chatsworth New Member

    I have an (old!) vaillant sine 18 combi boiler which requires a new diverter valve. Any idea how much this is likely to be anyone, please?
  2. mrj

    mrj New Member

    In my experience the valve almost never needs changing, they are very reliable.

    What exactly is happening?

    For instance, if you cant get any heating it could be nothing more than a slow dripping hot tap. This keeps a steady flow of cold water running over the wax capsule, this stays cold and thus in the hot water position.

    Another possibility is that the wax capsule has finally worn out, this can be replaced on its own.

    Sometimes the micro switches on the top come loose and move, this stops them from being activated when the valve opens to central heating mode.

    If the valve does need changing it is not a cheap item, last I heard they were a £200 or more plus about 1 to 2 hours to change it, depending on who's doing it.

    Martin
  3. Chatsworth

    Chatsworth New Member

    Hi Martin,

    Thanks for your reply. In essence the boiler is pumping water around the central heating system whenever the hot water flows (i.e. in the taps or when the shower is on) and is not diverting properly.

    I was advised the cost would be around 200 quid, so your price seems good, well not good but accurate. It just sounded a little expensive at the time and after some time googling for that particular component thats all. But if that is the going rate, that is the going rate!

    Cheers.
  4. Agile

    Agile Member

    Although they can get seized up the problem is usually the wax capsule. In any case if opening it up its wise to fit a new capsule.

    This work needs about 150mm clearance on the left hand side of the boiler and 300 mm underneath.

    We would charge about £146-£156 inclusive in the London area if those clearances are available. Its a tricky job and few people know how to do it, or even if they do, want the bother on such an old boiler.

    However the boiler, although 18-19 years old, is still a good performer and its always cheaper to fix it than to replace. A modern condensing unit would give 205 more hot water and save about 25% on gas bills.

    Tony Glazier

    Agile Services
  5. Chatsworth

    Chatsworth New Member

    Another quick question on this. I orignally had a heating engineer out to service my boiler and also look into the low pressure and the fact that when I turned on hot water, the radiators also started to fill - this is for a house I just moved into. The pressure was well below 1, infact is was 0.1 or 0.2! I was advised I needed a new diverter valve by the engineer.

    However, I have noticed that since it has been serviced and the system re-pressurised to the correct level, the radiators no longer come on when hot water is turned on. So, I am wondering, do I really need a diverter valve? What I wanted to ask was whether or not the low pressure itself could affect the valve function? Pressumably, the valve uses the water pressure itself in order to close and divert the flow, or does it? Can anyone briefly explain how this works and whether (in your opinion) a new diverter valve is neccessary or whether the low pressure could have been the cause. Many thanks
  6. Agile

    Agile Member

    The diverter valve switches the boiler on to provide heat when there is a demand for hot water preheat. It also diverts the primary flow into the secondary heat exchanger.

    The motive force to move the diverter comes from the expansion of a wax cartridge.

    If the boiler provides heating and hot water normally then it would be sensible to assume that there is no need to replace the diverter. If its not broken dont fix it!

    Tony Glazier

    Agile Services

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