Vaillant VCW 20/1 T3W No hot water

[gorselands]

No hot water with CH turned off.
Only noticed this the other day after a drain down to replace rad valve and some piping. Refilled/bled system all seemed to be fine HW and CH with switch set to CH. Finally decided to bleed main heat exchanger - no air or water came out. Checked bleed on domestic heat exchanger, again, no air or water. Turned switch to HW only and boiler did not fire. Problem could have existed for a while.

What's throwing me is what's stopping the water getting to MH/ex. and DH/ex. Valve or pin seized??

Any ideas as to where to start looking much appreciated.

Cheers

Mike

 

[The831Bunny]

What pressure does the pressure gauge read? No water OR air from a bleed point does not make any sense if you refilled it. You would have one or the other, unless the bleed point(s) are blocked, which is not impossible, but rare.

 

[gorselands]

Hi The 831 Bunny, good to hear from you. I was hoping you or Bunnyman would get back as you gave me so much help in the past when I replaced the flowswitch/divertor on the other boiler (big old House) Reading about 1 bar - there seems to be plenty of pressure as the 10th rad upstairs (furthest away) is blowing water out when bleed valve opened.

Mike

 

[gorselands]

After reading post, completely removed bleed valve on MH/ex and then prodded with a bit of thin welding rod - the water really squirted out, soaking me and the scullery. Repeated with DH/ex - same thing. There's definitely water there!!! Unfortunately boiler still doesn't fire when hot tap turned on.

Mike

 

[The831Bunny]

Can you hear a click when you turn the tap on? If not it sounds like the water section is not operating. Probable causes are perished diaphragm and/or seized spindle/gland.

In the short term try the pre-heat switch on (right hand switch) pressed in at the top. If the hot water works fine then with the heating off, deffo water section not operating. It will give you hot water without having to heat the house.

 

[gorselands]

Sure I can hear some feint clicking turning tap on but tap not near enough to boiler to be sure where from and no plumber's mate.

With preheat switch on and CH off still no HW.

Is it worth taking water section apart anyway? Cant remember if I need to drain boiler for this, would assume so.

Will look again in the morning when Talk Talk engineer has been to try to find out why snail mail is faster than my broadband during the day.

Thanks again for your help

Mike

 

[The831Bunny]

Ok, if it's not working with the preheat turned on, the flow switch HW micro switch needs adjusting.

When running the hot tap turn the mains OFF on the front of the boiler, take the alloy cap off of the flow switch and locate the 7mm nut on the spindle. Turn it clockwise till the right hand plate is 0.2mm (nearly touching) above the red micro switch body. You may find using a 7mm socket easier. Turn the power back on and check that when the boiler lights the heating flow pipe on the left hand side remains COLD. If it gets warm the flow switch has had it

 

[Bunnyman]

An if the flow switch has had it unfortunately so have u as obselete now,

 

[Agile]

There are often some wax elements still floating about. I still have about three left ( for my customers ).

If you wanted to spend money the whole unit used to be available at about £200.

By chance I am going to one of those old beasts tomorrow!

If they are not regularly operated, the piano key switch contacts often become high resistance. Repeatedly operating them sometimes gets them going again.

Tony

 

[gorselands]

Thanks gentlemen. Not sure what the 'piano switch' contacts are or where they are located - the three on the front of the boiler? Could you advise me? Problem may have existed for a while as I rarely use the hot taps to that boiler in isolation, i.e. hot water only.

Will try adjusting contacts to RH micro switch and test that heating flow pipe remains cold.

I do have a spare wax thermostat. Ordered it when I replaced the complete flow switch on the other boiler a couple of years ago. So the one I took off is cleaned and ready to rebuild.

Will check contacts, if flow switch wants replacing won't be till the weekend before I can tackle it but will let you know how I get on.

Again thanks very much

Mike

 

[Agile]

The piano key switch contacts are behind the keys but soldered directly to the PCB and so not acessible to clean or as a spare apart from replacing the whole PCB ( which do seem to be still easy to buy ).

If the wax element is not working then the microswitches are not going to be doing all that much depending on where it has jammed.

Failure to move is sometimes caused by the waxstat but also by the inside parts and/or the gland at the top being tight too.

Tony

 

[gorselands]

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

 

[gorselands]

Just reading up - Vaillant says not to use any grease or jointing compound on assembly. Probably best anyway to use new seals. Are they still available or a common size? May as well get prepared before starting.

Mike

 

[Agile]

You need a new diaphragm, they can sometimes be obtained.

The gland is available because used on other models!

Tony

 

[gorselands]

Hi Tony. I'm talking about the flow switch. Didn't think there is a diaphragm in that.

Mike