Viessmann Vitodens 200-W Problems

[Camperdown]

I have two Vitodens 200-W system boilers connected via a low loss header. They are about 7 years old and have run perfectly since they were first installed until now. They were installed as part of a whole house re-plumb and have had Fernox MB-1 Heating Protector in the circuit since day one.

One still works fine, but one keeps overheating with either an F2 or an F3 error. When they were recently serviced the plumber replaced the flame sensors and the spark ignition probes on both boilers, but that didn't solve the problem. His next suggestion was to start replacing parts until he figures out what the problem is, but given the cost of Viessmann parts, I wasn't keen on that idea, so I have tried to go as far as I can myself without touching any of the gas related parts.

I have flushed through the heat exchanger with water from a garden hose and got a small amount of magnetite out, but it seemed to be flowing freely. I removed the directional control valve (which isn't used because of the low loss header) and found it was completely caked in a hard shiny black deposit which took a lot of effort to break up and remove from the rubber. I have swapped the pumps over between the two boilers in case the pump was faulty, but the problem has remained. I don't think I can do anything more without having to disturb the gas side which I know is illegal.

When I fire up the boiler it sounds like a kettle boiling. The burner quickly regulates down from full output to low (based on the fan speed) but the temperature on the screen on the front of the boiler keeps rising until it his 92C when it cuts off. The pump keeps running and the temperature gradually comes down until it reaches 62C when it ignites and the same happens again. Every so often it goes over 100C and then trips with an F2 or F3 error.

None of the local plumbers seem to be experienced with Viessmann domestic boilers, so does anyone have any ideas of what the problem could be or anything more I can try before I get the plumbers back?

One final thing - while I had the system depressurised yesterday, I also thought I would check the pressure in the expansion tanks on both the boilers. In both cases when I pressed a pressure gauge onto the Schrader valve I got fountains of water spewing out of the valve. I guess that means both the bladders have failed as there shouldn't be any water in there. Am I right?

 

[Brambles]

Presumably you have no magnetic filter on the return to the boilers?

From the work you describe you have implemented, you have broken into the “room sealed” part of the boiler to access the heat exchanger. If so, the seals should be checked by a Gas Safe Registered engineer before you attempt to use the boiler.

Personally, I would not use any plumber / heating engineer who’s modus operandi is progressive part replacement. I am surprised that he / she did not start to strip down your working boiler to source parts on a trial and error basis.

F2 and F3 codes on Viessmann are generally a straightforward fix, but you will need a Gas Safe Engineer to implement it.

If your system is very dirty that needs to be addressed before you bring the boiler back into operation.

Viessman do a fixed price repair - but that may not be applicable if there has been no debris protection (serviced magnetic filter) fitted to the installation.

 

[ShaunCorbs]

Get them to remove and replace the rubber tubes

As for expansion vessel no, no water is supposed to come out

 

[Camperdown]

Thanks for getting back to me.

Both boilers actually have their own individual Fernox TF-1 filters on the return from the low loss header and there is one on the return from the heating circuit the goes around the house.

Thanks for confirming the expansion vessel questions - I thought so.

I will contact Viessmann and see what they can offer in terms of a fixed price fix, and otherwise I'll replace the expansion vessels and then get a Gas Safe plumber to replace the rubber tubes and re-check the seals.

 

[Gasmk1]

Get them to remove and replace the rubber tubes

As for expansion vessel no, no water is supposed to come out

sean is ther eany rubber tubes in the 200

 

[Camperdown]

There is a black rubber looking tube at the back between the pump and the back of the heat exchanger, with an automatic air vent half way along it.

It is hard and not flexible, so I don't know if it's rubber coated copper, or if it's rubber that's gone hard, but they is definitely one rubber type tube at the back (not including the condensate drain).

 

[ShaunCorbs]

the early 200s did have them gasmk1

op dont squeeze them just get them replaced