Viessmann vitodens 200-w. hot water icon dissapeared

[MP plumb]

Hi,

a client of mine has a viessmann vitodens 200-w system boiler. I have come to the job after 2 previous bodge job builders, so im now there to pick up the pieces. I have managed to fix all the problems but one...

The system has a 2 port valve for the hot water in a megaflo, and 3 2-port valves for 3 heating zones.

The hot water icon dissapeared a few days ago, and the hot wouldnt always come on with the programmer set for hot water demand (the cylinder was only luke warm so i know it should of been calling for heat)...so i changed the hot water motorised valve, incase it was being a bit intermittent. The boiler fired up and the motorised valve opens, suggesting everything was working as it should, but still no hot water icon.

The client has said today she is without hot water again but has put the immersions on.

i rung viessmann and one guy said something to do with relays? That is a bit beyond me with my experience, expecially with this boiler as i have never had to work on this make before. He was also saying stuff about the stat.
another guy said he didnt think the hot water icon should even be there.... But obviously is it or it wouldn't of been there all this time until now!!

If you know what the problem is, and if it is to do with the wiring or the stat, can some one explain it to me please?
thanks

 

[Howsie]

What controls are being used?

 

[MP plumb]

There is a cylinder stat that came with the megaflo, honeywell motorised valves, 3 room stats and a 7 day programmer for hot and heating.

 

[Howsie]

When we install these the hot water icon isn't used. Th boiler just gets a call of heat and the rad icon appears and the two ports do the rest.

 

[MP plumb]

It makes sense on a system boiler that the tap icon shouldn't need to be on. But the client said the icon used to be there, and if my memory serves me well, i think i saw the tap icon too. Any ideas at all will be appreciated, even if its a guess of the cause.

 

[MP plumb]

Howsie, do you work in london? If you have worked on these boilers before, i may have a job for you!

 

[Howsie]

Yep. We cover London and Surrey.

 

[MP plumb]

When i changed the motorised valve, i checked several times that the boiler would fire with the programmer set to auto or constant for the hot and every time it fired and the motorised valve opened. Its been 2 days and the boiler suddenly wont light again. It all seems to of gone wrong since this tap icon disappeared.

 

[Howsie]

Have they been fiddling? Have you tried removing the front panel completely and see what happens then?

 

[MP plumb]

No, i haven't. I understand that these boilers are much more high tech than a typical vaillant, so i fear the boilers ins and outs would be out of my knowledge

 

[Howsie]

With the front panel removed it should fire on a call for heat on the default settings.

 

[MP plumb]

Ok... What is that going to tell me though? Sorry if i sound like a dumb bum.

 

[MP plumb]

32 views... Some one must have an answer!!

 

[payney1974]

Is it the vitodens 200 system boiler with the internal diverter (separate flow and returns for CH & DHW, DHW gets priority over CH)? If it is the cylinder should have a Viessmann stat connected to it, this is why you get the tap icon appear. I would check ohms reading on this stat before anything else.

 

[MP plumb]

Ok thanks. If it is the stat, why would the boiler occasionally fire up and the valve open?

 

[payney1974]

I was thinking if you have DHW demand and cylinder is cold but no tap icon, I would check the stat first because the demand will go to the boiler first and then to the stat, if stat is out of calibration it may think the tank is at temperature. Is there a DHW timer on the Viessmann boiler itself? Can you set different DHW temperatures for different times? just a thought.

 

[payney1974]

When we install these the hot water icon isn't used. Th boiler just gets a call of heat and the rad icon appears and the two ports do the rest.

I thought you had to use the viessmann cylinder stat for this boiler?

 

[Howsie]

Nope.

 

[MP plumb]

Payney, if i hadnt of mentioned that the guy from viessmann talking about a stat would you of suggested it too? I will need to go back to the job to see what stat is installed in the cylinder. I know it could be just a coincidence that the stat has gone since we have been working on the system but it all seems a bit weird. Regards to a timer, i would have to say no, but not def. the programmer seems to control the whole system, not the boiler controlling.


i dont know if it has an internal diverter, it is the 200-w boiler though so that may confirm it?


thanks for your advice with the stat, is there any thing else you would suggest i try incase it is not the stat?


i want to go there and fix it in the one visit, instead of going back and forth.


thanks for your help.

 

[Roger Welton]

The 200W can work with or with out the internal diverter, it is required however if they are running weather comp from the boiler.