Vaillant VCW 242e Domestic Hot Water problem

[rwalters]

We have had an intermitent problem with our 15 year old Vaillant boiler for several months. Some days we cannot get domestic hot water out of the system. You can hear the pumps or something fire up in the boiler and a clicking sound but it does not fire. Other days it will be fine. We have had British Gas out on several occasions, but whenever they turn up the problem is not their.

We called them out a couple of weeks ago for the same problem, and luckily this time the problem was evident when the engineer turned up and he diagnosed that the diverter valve had got scale on it and was not functioning correctly. The next day he returned and replaced the valve and for the rest of the day the hot water was fine.

The next couple of days, hot water was intermittent again. I took a look at the boiler and saw a small micro switch next to the arm that comes off the top of the diverter valve. With the domestic hot water switched on and the boiler clicking but not firing,it you manually press this switch with your finger the boiler fires.

This micro switch has a small amount of adjustment on it, so I adjusted it slightly closer to the diverter valve arm and for about 2 weeks the boiler worked flawlessly.

Now it has started playing up again. Could it be the microswitch if faulty or could the fault lie elsewhere ?

The boiler is a Vaillant VCW 242E. Could anyone suggest anything, and if it is the microswitch, it looks relatively easy to replace, where would I go to source on.

Many many thanks for any replies.

Regards

Richard Walters

 

[weargas]

where exactly is the microswitch?

 

[rwalters]

Looking from the front of the boiler, the microswitch is just to the left of the actuator coming up from the diverter vavle

 

[weargas]

that's not the diverter valve. Is that the bit the BG engineer changed?

 

[kevplumb]

servo valve

 

[ChrisR]

Are you clear which bits are which? Diverter valve's on the right if I've got the right model, the central thing is the servo valve, from which about 4 thin tubes go over to the DV.
Which bit was changed?

 

[rwalters]

Sorry guys, excuse my ignorance. It sounds like the servo, the bit in the center of the boiler that has a piston that rises the more the hot water tap is opened. This server has an arm on the top that presses against a microswitch to the left of the unit. This is the switch that when you push it manually the boiler fires and heat the water, but doesn't seem to do it on it;s own.

British Gas replaced the servo unit.

 

[weargas]

well the new servo comes with a new microswitch fitted and adjusted correctly, so if the arm isn't hitting the microswitch you probably have a problem with the water section underneath the servo. A blocked/restricted venturi or split dhw diaphragm. It could also be limescale around the stuffing box and on the pin.

 

[rwalters]

I am pretty sure that the microswitch was not changed as part of the unit replacement. The British Gas engineer changed the unit that has the 4 or more pipes coming out of it. This part is all nice and shiny and new. The microswitch is still covered in fluff and dust so looks to me like it hasn't been changed.

 

[kevplumb]

as suggested ceeck for free movment of the pin

 

[rwalters]

The British Gas engineer replaced the unit because the pin wasn't moving correctly because of a buildup of limescale.

 

[kevplumb]

could be scale in the dhw exchanger

 

[weargas]

the servo comes with a new pin which i'm presuming he greased and fitted. Sounds like he hasn't addressed the problem of why the pin has scale on it in the first place. Most likely from a worn stuffing box leaking water. The repair can only be temporary because the problem hasn't been fixed properly.

So many engineers don't repair things properly.

 

[rwalters]

whereabouts is that kev ?

 

[weargas]

don't listen to that eedyut.