Vaillant VCW Combi problem and free beer

[blippy]

Hi – I have a Vaillant VC/VCW Combi boiler which provides heating for the bar area of my pub, and hot water to the public toilets. Unfortunately it’s recently started playing up. The boiler fires up no problem on both CH and DHW, but the output is way down – it seems to never get out 1st gear - if I understand it right this design modulates things right down for ignition, then ups the wick – this just doesn’t ever happen. Watching the burner confirms this.

I’ve had two local engineers come out to sort it, and both have taken one look and told me it’s not viable to repair due to its age. I’ve also had a good search of this forum, and it looks like the general opinion of these boilers is they’re built like tanks – you just need to find a engineer who understands their complexities to get them sorted when they do go wrong.

I’m in my first year of business and really can’t afford to replace it at the moment, plus it would have a major impact on my customers if I was forced to go down that road.

Can anyone give me any ideas where to look – I have an electronics background so should be able to diagnose control/sensor issues competently.

I’m afraid I can’t identify the exact model – I have no manuals and I can’t find anything on the boiler itself – but the lower panel inside is grey painted steel, with the two square dials on the right. It’s electronic ignition, and I think that must make it a VC GB 182 EH, a VC/VCW GB221 H, a VC/VCW GB 242 EH or a VC/VCW GB 282 EH.

Many thanks in advance for your help, and I’ll send a couple of pints of my best ale to anyone who can help me sort this one out

Chris

 

[ChrisR]

Vacuum pump packed up.
Just email me a couple of ciders.

How about a packet of dry roasted for a pdf of the manual?

 

[Agile]

I’m in my first year of business and really can’t afford to replace it at the moment, plus it would have a major impact on my customers if I was forced to go down that road.
Chris

I dont see why it would have an impact on your customers!

It may well be a gas related fault! Have you made sure all the gas taps before the boiler are fully on?

I cannot give you advice on gas parts inside the boiler.

Tony

 

[pannierstan]

Yep Chris is on the nail I would say. The impulse tubes tend to snap right where they enter the pump. You might be lucky if one of the pipes has come off!

Stan

 

[blippy]

Tony,

Yes, I checked all the gas taps are on fully.

The reason it would impact customers is because the boiler cupboard is at the end of a corridor with the doors to the toilets directly on either side – I’ve have to close for the duration of the install – and I have a significant number of Christmas Fayre bookings every day for the foreseeable future, so I’d have to cancel them.

I have a Corgi registered friend who does all the work on my kitchen equipment – he would be able to check burner pressures and the gas side of things if that would help diagnosis?

Chris and Stan - thanks - dry-roast and bulmers in the post

Thanks for your help,
Chris

 

[ChrisR]

Stan -or anyone - these boilers are before my time really
If the mod light's on bright and you don't have a high flame, the air pump should be running, right?
ANy idea what voltage it runs at or what pressure it should produce? In other words how do you diagnose between a bust pump and a bust gas valve?

 

[blippy]

OK, I had the burner pressure measured today, and we’ve established that there is a very minor step up in pressure when the green light comes on on the control box – i.e. when the diaphragm pump is pumping. I’ve checked for disconnected vacuum tubes etc. and all is as it should be.

My Corgi matey tried to adjust the burner pressure for max modulation by rotating the R/H screw on the Operator as per the MIs – this does absolutely nothing with either both control tubes dc’ed or both connected. The L/H screw adjusts the min pressure within acceptable range.

So, question is, is the Operator knackered, or could it still be the diaphragm pump not pumping up to pressure. Does anyone know what pressure the pumps are meant to run at? I’m pretty sure that the pump is either on or off, as signified by the presence or lack of the green LED. Does anyone know if this is the case or not?

Thanks to all who have helped so far, I now know loads more about this boiler than I did a week ago, and I’m confident that I can get it up and running with your help

Cheers,
Chris

 

[Agile]

The gas valve is the same or similar to one used on a Glow Worm where the fan venturi provides the pressure to "enable" the gas valve.

This is only usually 2-3 mb so far less than the 40 mb which you can blow with your mouth.

A VERY gently blow by mouth should be enough to operate the gas valve.

A CORGI would measure the pressure from the diaphragm pump. A less technically minded CORGi might blow down the tube ( and risk damaging the gas valve ) and see if that brought the gas valve back on.

However before getting too involved, has anyone tested the incoming gas pressure at the gas valve inlet?

Thats the first basic test and often identifies the fault before too much time has been wasted.

Tony

 

[ChrisR]

SO what is the pressure which should be generated by the pump - as opposed to the venturi?
I have one somewhere, could measure it I suppose!

 

[blippy]

Tony, Chris,

I'll get my chap back to measure:

1) the inlet gas pressure
2) the pressure on the fan control line
3) the pressure on the diaphragm pump control line

Once he's done I'll report back. Might be tomorrow now as I don't know what jobs he's got on.

One thing I didn't mention before is that the appliance is LPG. Not sure if this is significant (other than I know all the pressures will be different).

Thanks again for your suggestions.
Chris

 

[Agile]

As your CORGI fellow does not seem very good ( otherwise he would have found the fault ) its important when measuring the inlet pressure that its the "working pressure" as measured with the boiler running!

I hope he is CORGI for LPG ??? Otherwise he will have no idea of what pressures to look for.

Its makes little difference that its LPG except than there are more potential causes of low working pressure. You should have told us though.

Tony

 

[namsag]

Agile why is his guy no good .Did you not say this boiler Baffles people and on other occasions you have called it one of the most complicated about or are you just trying to look clever again.

Presuming 37mb inlet pressure from lpg the
if it is a 242e its ignition pressure is 4.4mb and maximum pressure23mb
If its a 282e its ignition pressure is 4.6mb and maximum 24 mb
Ntc lead should be removed so burner does not modulat during pressure setting

Also if ntc is shot it will stop burner coming on full blast so if when you remove lead burner flairs up full it will be a faulty ntc.

Sorry can`t tell you what the pump pressure should be

 

[blippy]

Gents,

The guy who is helping me out deals exclusively with commecial kitchen equipment, which, suprise, suprise is all LPG in my establishment. He is extremely competent, but hasn't worked on this particular boiler and it's complex control systems(s) as he's not a domestic heating specialist!

I'm assuming that the working inlet pressure should be about 38 mbar for G31?

He's coming out tonight after work to test it for me.

Hope this helps,
Chris

 

[namsag]

Ignition pressure must be set within first 5 seconds if not turn it off an redue. The green led comes on as it goes to maximum pressure and this is when that pressure should be set

 

[blippy]

Thanks namsag,

My Corgi matey did as you suggested yesterday when we tried to set the pressures, plus we also removed the banjo connection from the diaphragm pump which effectively keeps the boiler in ignition mode. Having done this, we double-checked the ignition pressure in the first 5 secs after CH demand was established.

The ignition pressure is set at about 4.5 mbar, as per spec, and it jumps to about 6 mbar when the green LED comes on. But this is way short of the 23 mbar it should reach.

I'll post the other pressure readings when I get them later.

Thanks again,
Chris