Vaillant combi boiler using gas when cold water running.

[face]

Hi,

We had a complete new central heating installed about 2.5 years ago now with a Vaillant combi boiler. Everything seems to be working fine but I have noticed something odd this morning.

I have been monitoring our gas/elec usage for the last few weeks which is what prompted me to notice this.

When I run the COLD tap in the kitchen, if I go and stand near the combi boiler in the utility room, I can hear what I think is the water going through it. The water coming out of the kitchen tap is indeed cold, but the gas meter is is increasing. Not by a lot - about 3/1000s for 10 secs of cold water.

Is this right - or is there something wrong? I wouldn't have thought it very green to have a combi boiler using gas when you are drawing cold water.

I am going to check all the other cold taps in the house tonight and see if any others do it. I would have thought that they all will though, won't they?

Any info or help would be gratefully received.

Many thanks in advance,

Face

 

[45yearsagasman]

Exact model would help.It may be water preheat has been activated or just that you haven't noticed it operating before.

 

[face]

Wow - thank you for the quick reply!

I think it is an EcoTec model - I will post the model number when I get home. I'm pretty sure that the pre-heat option is turned off but I will double-check this also.

The Flame symbol doesn't appear on the boiler's LCD display when it happens.

I'm just concerned about where the gas is going for safety reasons.

Thanks again

Face

 

[Agile]

If you are competent to do so you can turn off the gas valve on the pipes under the boiler.

It does sound very odd and you may have a gas leak.

Is the meter really only turning when the cold tap is turned on? Thats very odd so please keep us informed.

You may need a competent engineer.

Tony

 

[onlyfitidealboilers]

are you on a water meter??

these boilers have an aqua flow sensor, which may be activated when you swith your cold tap on or off. resulting in fireing the boiler

try fitting an expansion vessel to your cold water supply, you might just find that sorts it good luk

 

[Agile]

But he says there is no flame symbol.

Another test he could do is run the CW and feel the flue outlet and see if the boiler fan is on and if its warm.

Tony

 

[face]

Hi everyone,

Thank you all for taking the time to reply.

I've now been round all the cold taps in the house and I just cannot get it to happen again. Sort of.

After I'd tested all the taps a couple of times, I did notice this - I had the cold tap on in the utility room and as I turned the cold tap off, I heard the boiler make some noise so I turned straight round and the flame symbol was on - very briefly, probably less than a second, then it disappeard but the pump symbol was on.

So I checked the gas meter and it had increased by about 2/1000s which I gues was the very brief time the flame was on.

Also, oddly, I also couldn't hear the sound of the cold water running through the boiler any more - yet both my wife and I are convinced that we have heard it previously.

But, apart from that one very briefly moment, the gas meter doesn't seem to be responding to a cold water draw at the moment.

I'm going to keep an eye on it though over the next few days, just to make sure.

One quick question though - does the "once-every-24-hours-anti-seize--start-up" just fire the pump up or would it also light the flame? Was wondering if it was just a coincidence?

Thanks again,

Face

 

[Bunnyman]

U can get a non return valve fitted into the mains cold before the boiler this will stop it there is an air deadleg d somewhere in the System prob where the old cylinder was takin out

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• Bunnyman
• 26 Mar 2010
• 499

 

[holty]

would of said the NRV would be better on the hot outlet. so as some form of expansion.back to the cold.

 

[Bunnyman]

Nah gotta b on cold main inlet. As u turn the cold tap off it causes a small pressure fluctuation that nudges the impellor in the aquasensor or fit a small expansion vessel

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• Bunnyman
• 26 Mar 2010
• 499

 

[holty]

fair enough bunnyman, i usually fit on the hot outlet which usually solves the problem, yet never had this on the ecotec so ill heed your advise.

 

[Bunnyman]

Hi holty u can also reduce the sensitivity of the aquasensor in the electronics this is the cheaty way of doin it but gets round the problem

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• Bunnyman
• 26 Mar 2010
• 499

 

[Agile]

I would always fit it on the outlet too.

On the inlet it risks causing expansion problems if nothing is leaking.

Tony

 

[2point8ghiax]

Sorry to hijack slightly. My brother's Ecotec does something similar. When you turn the cold tap off, you can hear something running (poss fan) in the boiler.

So the opinions are NRV on the hot water pipe out of boiler? If an expansion vessel is used instead, which one, and where is it to be fitted?

 

[Agile]

It needs an NRV.

Its not an expansion issue. It can expand back down the mains.