Vaillant boiler - short circuit - pure floor heating

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17 Oct 2021
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Country
Denmark
Hi DIYnot,

Firstly, i will apologize beforehand as my english is not perfect. I am from Denmark, seeking some guidance as i haven't managed to find a plumber or a boiler technician who can help me with my problem.

I have had a bigger renovation project where i switched from radiators as a primary heating source over to pure floor heating.

When heating demand required, the flame turns on for only 10 seconds and then shuts off. I have had several plumbers and boiler technicians over, but nobody seem to have the knowledge of the issue. I have had a talk with Danfoss which advise me to add a automatic bypass valve, but i really don't know if it helps.

I have added a diagram of the installation together with a video of current situation.


PFcZsOF
https://imgur.com/a/PFcZsOF
Can somebody guide me?

Both circulation pumps are running.

Vaillant EcoTEC Exclusive
VC206
D0: 4 kW
D2: 5 minutes
D40: 40
D41: 30

Minimum temp. 30°C
Max. Temp. 50°C
Pump pressure: 250mbar
Differential pressure: 170 mbar
Flow: 650 l/h

Floor heating
Fully balanced system
9 circuits
480m in total length

Design
Heating demand: 3955 W = 4kW
Flow: 426 l/h
Pump pressure: 0,042 bar
Supply temp. 42,1 °C
Delta T: 8°C

upload_2021-10-17_10-58-7.png
 

Attachments

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I would check to make sure no valves are currently in the off position, easily done, including under the boiler (flow and return).
 
How have you connected the ufh call for heat as it looks like your using vaillants ebus control.
 
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You cant mix the ebus and 240vac controls without some type of interface, the op needs to tell us how the ufh pump is being controlled ,it could be the ufh actuators taking too long to open and the boiler just dead heading.
 
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How have you connected the ufh call for heat as it looks like your using vaillants ebus control.

No, there is no wiring between my underfloor heating and the boiler. The boiler supposed to start when return temperature of boiler is below adjusted minimum setpoint when the weather compesation controller is installed.

I disconnected the weather compensation controller and the boiler regulates fine in 1-2 minutes between 40°C in test mode S.09, but once it's going into regular heating mode S.40 it simply can't regulate and goes way above supply temperature setpoint. Once it's in S.40 it's sounds like the fan is running too fast and also there is weird water sound.

Please take a look at this video showing once its in S.09 Test mode and in regular S.40 heating mode.


Br
 
Your boiler will run if you remove the weather comp because the 24v link is in place, put the controller back on the boiler, could you tell me how the shunt pump is being controlled ? I am also assuming you have removed the actuator heads from the ufh manifold.
 
Your boiler will run if you remove the weather comp because the 24v link is in place, put the controller back on the boiler, could you tell me how the shunt pump is being controlled ? I am also assuming you have removed the actuator heads from the ufh manifold.

I am not sure which 24v link you are refering to is? My UFH shunt is being controlled with Danfoss Icon which is a controller communicating with seperate thermostats located in each room/zones. The pump (UPM3 Auto L 15-7) on the shunt is running at a constant pressure (setting 2).

NnNBfi8


upload_2021-10-18_22-57-41.png
 
We dont have your type of system here in the uk, all boilers have to have an interlock (they cant fire unless there is a call for heat) I cant see how your system can work properly without some sort of control between the ufh and boiler.
 
All,

Its now fixed. It showed S40 which Vaillant said was CO sensor. They came, replaced it with a new one free of charge. It now runs smooth.

I have also wired cable between boiler and ufh so it can call for heat.
 
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