High pressure into the boiler

[yumera]

Hi All,

We have issue with our "viessmann vitodens 200" (16 year old already), about a month ago display was blinking with message "F E" and the whole system was off.
After resetting the system it get back to normal work, but then we notice that there is a high pressure on the gouge around 2.5 bars. And it was keep raising.
I have release the pressure from the valve under the control panel to 1 bar. But by keeping eye on it every day pressure is going up slowly by 0.1 bar.
Another strange behavior i notice is that when temperature it's going down slowly : 75, 74, 73 ... 30C.
Before the mentioned error, display was only showing temperature when water is heated at 75C once is done it was only showing 30C and keep it that until next heat starts.
This is now the second time i have release the pressure, and the issue is not appear to be solved.
At the beginning i suspect a high pressure valve (the one which fill out the boiler), and arrange a technician to check and replace if needed. But at the arrival of the technician, we saw that valve is working as it should. Technician then hit me with the news that the whole boiler is need to be replace as her they do not repair any of the "DHW cylinder".
It's not cheap part to be replaced, and wondering if there is no other way that just replace the whole boiler.
Could anyone can give an advice in this situation?

 

[oz-plumber]

Just turn the inlet valve off and see what happens to the pressure.
It will increase and the water temperature rises, but should settle back to @ 1 Bar when cold.
If you're losing water pressure either leak, PTR valve faulty or expansion tank.
Temperature problems - faulty sensor or thermistor, or PCB.

Being that the boiler is 16 years old, many repairs are a costly mistake due to the cost of parts and repairs.

It may be a simple problem - get another opinion.

 

[SJB060685]

If your pressure is rising while heating and slowly returning to normal as the system cools then i would suspect the expansion vessel has failed first off. This is a straight forward repair in the right hands and definitely doesn't require a new boiler. As mentioned above one would also need to rule out the filling loop letting by to be sure that isn't adding to the problem.

 

[yumera]

If your pressure is rising while heating and slowly returning to normal as the system cools then i would suspect the expansion vessel has failed first off.

It is exactly what is happening, i have set the pressure to exactly 1 bar, then turn the hot water on and let the heating to start. Pressure raise up to 2,5 bars with a temperature = 75C. And stays like that for 5 min.
In about 5 minutes pressure has start to dropping off with 0.1 bars every minute at the same time with the temperature going down with 5C. Until again reach out 1 bar and temperature of 30-35C.
I was helping to the technician at the visit, by opening the high pressure valve and closing the whole water at the house. Then we slowly start opening the water and we could see that valve was realising a water.
After that test technician suggest that it's issue with "boiler" (by pointing to the big tank with water) but i guess he meant "expansion vessel", which for him is not repairable and need to be replaced with a cost of approximately = 1700 GBP, or complete new gas boiler system.
Also he warn me to have in mind the age of the overall system and all the repairs are expensive.
Thank you very much for the responses, now i have a overview and will think what we will decide.

 

[SJB060685]

Everything you said points to an expansion vessel problem, it could just need recharging, or it could need replacing and as I said certainly doesn't need a new boiler. I would seek the advice of another engineer

 

[oz-plumber]

You could get a new boiler installed for what the tech is quoting for the replacemnt of the expansion tank.

Find someone else to give you a price