Vaillant Combi Boiler Issue

Is it a VCW 242 and is this "diaphragm" in a black plastic enclosure at the bottom centre of the combi, operating a red microswitch via a little mechanism coming from the black plastic enclosure? I think that there may be some metalwork directly below the black plastic actuator, a valve, from which a shaft going to a temperature dial emerges ( calibrated 0-9 I recall )? I shan't go on in case it ain't the model I'm thinking of, le me know,

Andy.

In message , Dave Clark writes

Well, you need to find out the model of your boiler. Is it a Sine 18 or a 242E (H) for example? They're completely different boilers

The model is fairly helpful in these matters! VCW models I am quite familiar with. Theres a good chance it is one of them. (Enammeled metal casing, two hinged doors, lots of 4mm diamter pipes inside? Try looking from underneath for a model name?).

There is a diaphragm valve which _initiates_ the process of water heating. This valve moves a micro switch and operates another valve. The actuator pin can become stiff and fail to reliably move the switch and/or the valve in responce to the water flow. Unfortunately it requires a significant amount of disassembly to get at the pin to help it move.

AFAIK boilers are not made with a selection of diaphragm sizes if the diaphragm is only 1" then that the right size! On VCW the diaphragm is about 2.5" diameter however the valve it moves (which could be mistaken for another diaphragm valve) looks like it might hold a 1" diaphragm. In fact it doesn't, it reverses the action of the pump pressure via 4 x 4mm pipes upon other components.

The boiler should light up for water heating at a modest flow rate.

HTH

Thanks for the all the replies.

I have searched for the boiler model underneath but can't find it.

However, I am pretty sure that it is a VCW242 or 282?? The only reason is because the boiler engineer accidentally left the manual and your description of VWC models fits ours exactly.

I am also pretty sure that the 'diaphram' is the one that you are all describing.

Therefore, any ideas why twice in 10 days the hot water stopped, only for it to come back again later on in the day. When it failed, the pressure / flow rate through the hotwater tap was a lot less than usual.

Many thanks

Sounds like the diverter valve sticking -- you should be able to see it moving through one of the inspection holes if it is working properly.

Now, if anyone can give me ideas on why my later Vaillant combi still makes horrible clonks whenever the diverter valve operates i'd be very grateful :-)

G.

As a wild guess I'd say that the diverter valve is sticking and/or has a split diaphragm and possibly you have times when the water supply is low. Which means that at those times the there is a chance the boielr won't fire.

AFAIK there is no active control of the flow rate by the boiler. The DHW temperature knob (always stuck immovable IME) is simply a flow restrictor: the less flow the grater the temperature rise.

Funnily enough the DHW temperature knob on my now junked VCW242 was stuck immovable!

BTW my installation of a Vaillant Turbomax 828 to replace it went OK, thanks to all those on this board who helped with my queries. The worst bit was getting the pipes through the cavity wall ( moved the new boiler to an outside loo location ).

Worst screw up was finding out the hard way that a single drop of water left in a system when fitting solder joints will screw up any chance of getting a sound joint.

Second worst screw up was not realising that mild flux and end-flow fittings do not work well together. I thought that brightening the copper end of the pipe with wire wool would obviate any problems, but it turned out ( obvious really ) that you needed to brighten the inside of the copper fitting as well! I eventually used a much more active flux ( Everflux ) and abraded any copper surface which was going to have solder flowing over it.

Andy