Vaillant VCW 20/1 T3W No hot water

[Agile]

Sorry, they use rather different terminology to the generic parts.

I thought you were talking about the water section underneath which has a pin on top which activates the DHW demand microswitches. That has a diaphragm which usually is failed.

Tony

 

[The831Bunny]

Done all that has been suggested. The spindle (flow switch) is not operating the H/W micro switch. When M/S pressed down manually H/W (only) works and boiler flames. Heating flow pipe remains cold, only warms up with CH only on.

So am I right now in thinking it is the flow switch - either seized gland or more likely wax thermostat? Unable to move spindle in F/S down manually even with some pressure applied.

As I said, it will be the weekend now. And I may as well take the H/ex off and flush it. Think I can just drain boiler and DH/Ex. to do this.

Mike

Did you turn the 7mm nut down Mike? Also does the switch plate above the right hand micro switch rise up when the heating is on? It's quite slow anyway but you can speed the operation up by turning off all the rads on the TRVs or control valves. If the plate rises up after 5 minutes or so then the wax stat sounds ok. Turn on a hot tap and the plate should drop and contact the micro switch. If it falls short turn the 7mm nut down as I said above.

 

[Agile]

I am not convinced that his water section is operating the DHW demand switch.

Tony

 

[gorselands]

Thanks for the replies. Have to go out now, not back 'till late so will look at things again tomorrow. I did turn the 7mm nut as you said but will check that it rises. Spent ages on the phone trying to find washers and seals for F/S with no luck. So don't want to dismantle if it's not that.

Mike

 

[gorselands]

Head spinning! I did turn the 7mm nut down and a bit more this morning. Switch plate does rise but very slow.

Took panels off adjacent (GOOD) boiler to compare.

With boilers off for 10 minutes:-

PROBLEM boiler - RHMSP (right hand micro switch plate) still in contact with M/S (rising slowly). (sounds like the weather forecast) LHMSP clearance 4 mm.

GOOD boiler - RHMSP risen clear of M/S. LHMSP 4 mm clearance between M/S.

Central heating on and boilers flamed:-

PROBLEM boiler - RHMSP rises 0.5mm, LHMSP hardly rises and not in contact with M/S.

GOOD boiler RHMSP rises 8 mm. LHMSP in contact with M/S

The action of the F/S spindle in in the problem boiler is very sluggish and not rising and falling like the the one in the newer flow switch.

Thanks

Mike

 

[gorselands]

Meant to say that when I operate RHMS manually with H/tap running and CH off - boiler flames.

Mike

 

[Agile]

I thought that boiler only fires up if water section SW is activated by water flow AND if the RH SW is activated ( meaning pressed down by the lever because the wax element is cold ).

The RH SW has two connections and is NO. The original SW only has the two connections and is red in colour.

If there is no DHW flow and the CH is on ( or the DHW preheat is on ) then the pin in the flow switch ( or diverter valve as I prefer to call it ) should rise so the RH SW is off and the LH SW is on !

If under those situations the pin does not rise then either the gland is sticking or the wax element is not working.

Tony

 

[gorselands]

Hi Tony. I suspect the wax element is on its way out (27 years!) Flow switch is the term Vaillant use though diverter valve seems more common.

As the seals and washers are no longer available I was thinking of just removing the thermostat housing as the element came with three internal rubber seals. I would prefer to strip the flow valve completely and clean but the washers and seals are a problem - any thoughts?

Mike

 

[The831Bunny]

Hi Tony. I suspect the wax element is on its way out (27 years!) Flow switch is the term Vaillant use though diverter valve seems more common.

As the seals and washers are no longer available I was thinking of just removing the thermostat housing as the element came with three internal rubber seals. I would prefer to strip the flow valve completely and clean but the washers and seals are a problem - any thoughts?

Mike

I'll post a list of washer part numbers later. All readily available. I wouldn't bother stripping flow switch, 99% wax stat replacement will sort it mate.

 

[gorselands]

Thanks the 831 Bunny. The wax stat has three internal rubber seals with it. If careful I could use the existing washers with a bit of Fernox LS-X, though new would be better.

While I'm at it and in view of the skin of limescale behind the bleed points may take the MH/ex off and flush it using my homemade 'pop bottle and tyre inflator circulating pump'.

Mike

 

[The831Bunny]

//media.diynot.com/99000_98749_61336_17149242_thumb.jpg

Washers needed to change a wax stat in situ are: 3,5,&6 are included with the wax stat. 2x24 (Part No. 980223) thats it.

Turn off power switch, cold and heating isolation valves.

Drain boiler cold/hot circuits and primary circuit.

Undo the two cold connection nuts on the base of the flow switch.

Use a long flat blade screwdriver from underneath the cold water housing on the flow switch and remove the three screws. Be ready to catch a bit of water.

Remove the wax stat from the housing (a sharp tap through the base with a screwdriver will dislodge it).

Make sure the small rubber washer isn't stuck up in the main flow switch body and then insert the new wax stat in the cold connection base using the 3 new rubber washers. Refit to main flow switch body with 3 screws. Look for red stamp on body to ensure correct orientation or mark before disassembly.

Connect the cold tubes to the base using new washers as above. Turn on cold and check for leaks. run hot tap to purge air.

Adjust 7mm nut on flow switch spindle so plate just sits against right hand microswitch (important).

Refill primary circuit, vent, turn mains switch on re-vent and test.

Failing that call Bunnyman lol!

 

[The831Bunny]

Sorry that picture came out rubbish on my last post.

Try this: View media item 61336

 

[Bunnyman]

U should be a trainer 831 that's a very good instruction

 

[The831Bunny]

U should be a trainer 831 that's a very good instruction

I missed my vocation lol. I reckon the amount of wax stats being replaced now in the country you could count on one hand, and Tony's squirrelled 3 of them away lol

 

[Bunnyman]

Yep remember when we were doing 1 a day ,