Viessmann Vitodens 100W running hot and cold

[bojay]

Hi everyone hope someone can help. We have a self build house and had a Viessmann recommended plumber fit our boiler and central heating system nearly 2 1/2 years ago. As we are still building the house, although living in it we have only recently had a kitchen sink fitted. We had noticed from when the boiler was fitted that it had always run hot then cold in the bath but put it down to either the bath taps (temperature controlled) or the way the boiler worked. We now know this is not correct and the hot water should be constant.

We have a five year warranty from Viessmann but they keep saying it sounds like an installation problem and if they come out and it is they will charge us £90.00 so we contacted our plumber who came out to the house and said it was the plate to plate (whatever that is) and to call Viessmann to replace it - we called Viessmann but they sstillinsist it sounds more like an installation problem. We went back to the plumber and he said he didn't say that at all he now says its the way we are requesting the water i.e. not at full flow (who washes up at full flow!)

We have again tested and ran the water at half flow on the garage tap which is only about 8ft away from the boiler it ran hot for two buckets with the tap symbol on the whole time then the tap symbol went off and the water ran cold.

Sorry for such a long story but can anyone help/advise as we do not think it is fair we should be out of pocket for this.

 

[Phill Peck]

Before the tap diss appeared what temperature was shown on the screen

 

[bojay]

Hi it was around 60 degrees

 

[Phill Peck]

It's not a plate problem then

If the tap is dissapearing then it's probably a flow sensor fault which will be covered by your warranty

 

[Agile]

Half and full is not very scientific!

You need to measure the actual flow rate in litres per minute.

The boiler should switch on for DHW at about 2 litres per minute!

Tony

 

[superman123]

this has been a problem since installation, could be possible reverse circulation when running hw feel the cold mains pipe going into the boiler for a rise in temp to confirm

 

[Phill Peck]

It did pop into my head if hot and cold were reversed

Hot pipe should be 2nd from left
As in from left to right

Flow
Hot
Gas
Cold
Return

Run a hot tap and check the correct pipe is hot

 

[holty]

isolate the cold supply iso on the boiler. run a hot tap then tell us what happens.

 

[holty]

mysteryman. would be easier to check the benchmark thats filled in, for serial number . wont it

 

[bojay]

Thanks all for your replies I will do as asked tomorrow and post again

 

[bojay]

Hi I have checked left to right - all correct. Holty I turned off the cold feed on the boiler and turned on hot tap - no water coming through.

Thanks

 

[Phill Peck]

That should rule out incorrect pipework or reverse circulation

 

[holty]

just reread your post and a few things. when you say the water went hot then cold. is that a from start up. e.g the water will go hot then cold then hot again then continue to run hot. is the water runing hot then cold then hot then cold etc. is this your first experience with a combi?

 

[Agile]

He said earlier that the demand ( tap symbol ) goes off after a few minutes.

Sounds like a dodgy demand switch ( or even a PCB fault! ).

Tony

 

[mysteryman]

Quite likely a bit of debris in the domestic flowswitch. They are very different on WB1A and WB1B boilers. That's why he needs the serial number - which may or may not be on the Benchmark certificate.