Vaillant ecoTEC plus 831

Questions and Answers

A
Albert BakerAug 25, 2025
Why won't my Vaillant Boiler start?
- B
  Brandon HernandezAug 25, 2025
  If your Vaillant Boiler fails to ignite, it could be due to faults in the gas supply, such as a defective gas meter, air in the gas line, low gas flow pressure, or a tripped fire protection tap. It can also be caused by issues with the gas fitting, incorrect gas setting, a defective igniter, interrupted ionization current, faulty earthing, or defective electronics. Diagnose and rectify issues in the gas supply and fittings.
Q
qmaldonadoAug 31, 2025
Why is there no pressure change when the pump turns on in my Vaillant ecoTEC plus 831 Boiler?
- R
  Raymond MorganSep 1, 2025
  If no sudden change in pressure is detected when turning on the pump in your Vaillant Boiler, it could be due to a defective water pressure sensor or pump, or too little water in the appliance. Ensure sufficient water supply and inspect the pump.
W
wayneparkSep 1, 2025
What to do if the drinking water outlet probe stopped in my Vaillant Boiler?
- J
  Jordan CarpenterSep 1, 2025
  If the drinking water outlet probe has stopped (
I
isuttonSep 2, 2025
Why does my Vaillant Boiler show a flame when the gas valve is off?
- C
  Cathy ShawSep 2, 2025
  If your Vaillant Boiler shows a secondary light, where the ionization signal reports a flame even when the gas valve is turned off, it could be due to defective gas solenoid valves or a defective flame detector. Inspect and replace the gas valves or flame detector.
L
Lawrence BatesSep 2, 2025
What causes a short circuit in the tank sensor of my Vaillant ecoTEC plus 831?
- C
  Christine BauerSep 2, 2025
  A short circuit in the tank sensor of your Vaillant Boiler can be caused by a defective NTC, an earth leak/short circuit in the cable loom, or a damp plug connection. Inspect and replace the NTC or repair damp connections.
A
Anthony HillSep 3, 2025
What does it mean 'No valid DSN in AI and/or BMU' in Vaillant ecoTEC plus 831?
- S
  Steven GibsonSep 3, 2025
  If your Vaillant Boiler displays 'No valid DSN in AI and/or BMU', it indicates a spare part failure where the AI and motherboard were interchanged at the same time. Replace faulty components to resolve DSN issue.
J
Jason RomeroSep 3, 2025
What to do if my Vaillant ecoTEC plus 831 appliance does not start and ignition fails?
- L
  Lisa WilcoxSep 3, 2025
  If your Vaillant Boiler fails to start and ignition attempts fail, there may be faults in the gas supply, such as a defective gas meter or gas pressure detector, air in the gas, gas flow pressure too low, or a disengaged fire protection tap. There may be faults in the gas valve, wrong gas setting, defective igniter (ignition transformer, ignition cable, ignition plug), stopped ionization current (cable, electrode), faulty earthing in the appliance or defective electronics. Inspect the gas supply and ignition components for faults.
N
Nicole PetersSep 4, 2025
What to do if the flame goes off during operation of my Vaillant ecoTEC plus 831 Boiler?
- T
  Timothy SantiagoSep 4, 2025
  If the flame goes off during operation and subsequent ignition attempts fail, it could be due to a temporarily stopped gas supply or faulty earthing of the appliance. Check the gas supply and earthing connections.
M
Malik ConradSep 4, 2025
Why is there a dry fire in my Vaillant ecoTEC plus 831?
- L
  Lauren MeyersSep 5, 2025
  A dry fire in your Vaillant Boiler can occur due to too little water in the appliance, a defective water pressure sensor, a defective cable to the pump or water sensor, a blocked or defective pump, or a pump output that is too low. Ensure sufficient water supply and check the pump and sensors for faults.
C
cheryl07Sep 5, 2025
What to do if my Vaillant ecoTEC plus 831 shows water shortage and large temperature difference?
- J
  Julian BurnettSep 5, 2025
  If your Vaillant Boiler indicates a water shortage and a large temperature difference between the flow and return NTC, the pump might be blocked or defective, the pump output might be too low, or the flow and return NTCs might be interchanged. Check and unblock or replace the pump and verify the NTC placement.

Summary

Introduction

Notes on the Documentation

Information on the documentation provided for the appliance and general notes for clarity.

General Notes

General information about the boiler's design for sealed central heating systems and mounting.

Boiler Specifications

Technical Data

Detailed technical specifications including output, dimensions, electrical data, and performance figures.

Dimensions

Diagram showing the overall dimensions of the boiler and key connection points in millimeters.

Installation

Diagrams illustrating the function elements of combination and system boilers for installation.

General Requirements

Installation Site

Guidance on selecting a suitable location for the boiler, considering clearances and environmental factors.

Gas Supply

Requirements for the gas supply, including connection, pipework size, and leak checks.

Electrical Supply

Details on the required electrical supply, connection methods, and safety precautions.

Boiler Installation Sequence

Required Minimum Distances;Assembly Clearances

Specifies the necessary clearances around the boiler for installation and servicing.

Gas Connection

Instructions for safely connecting the gas supply to the boiler, including required tools and checks.

Heating Connection

Guidelines for connecting the heating flow and return pipes to the boiler, including pressure relief valve.

Electrical Connection

Detailed instructions for making the electrical connection to the boiler, including wiring diagrams.

Controls

Vaillant Controls and Accessories

List of Vaillant compatible controls and accessories with their connection details.

External Electrical Controls

Information on connecting external electrical controls like time switches and thermostats.

Connection Details for External Time Switches and Boiler Terminal Strip

Schematic showing connections for time switches and room thermostats to the boiler terminals.

Commissioning Part I

Preliminary Electrical Checks

Checks to be performed on the electrical installation before commissioning the boiler.

Gas Supply

Inspection, leak checks, and purging of the gas installation according to regulations.

Filling and Bleeding the Heating System

Procedures for filling the heating system, including checks and bleeding air from radiators.

Initial System Flush (“cold”)

Instructions for flushing the heating system to remove installation debris before boiler commissioning.

Functional Checks (Commissioning Part II)

Functional Checks

Procedures for performing functional checks on the appliance after installation.

Heating

Steps for checking the heating operation, including status indicators and display readings.

Handing Over to the User

Guidance on instructing the user on safe operation, controls, and the importance of regular servicing.

Inspection and Maintenance

Initial Inspection

Recommendations for regular inspection and servicing of the boiler for safe and efficient operation.

Maintenance

Overview of inspection and maintenance tasks to be performed annually and as part of regular servicing.

Servicing the Burner Module

Detailed steps for removing, cleaning, and refitting the burner module components.

Troubleshooting

Logical Fault Finding Procedure

Step-by-step procedure for diagnosing and resolving potential issues with the boiler.

Status Codes

Explanation of status codes displayed by the appliance to indicate operating conditions.

Diagnostic Codes

Information on accessing and interpreting diagnostic codes for fault analysis and parameter adjustment.

Parts Replacement

Safety Instructions

Crucial safety instructions to be followed before replacing any component to prevent damage or injury.

Replacing Burner

Procedure for safely removing and refitting the burner module, including necessary checks.

Replacing Fan or Gas Valve

Steps for replacing the fan or gas valve, emphasizing safety and correct reassembly.

Recycling and Disposal

Vaillant Service

Appendix

EC Declaration of Conformity

Document confirming the appliance's compliance with relevant European directives.

Vaillant ecoTEC plus 831 Specifications

General

Model	ecoTEC plus 831
Category	Boiler
Output	31 kW
ERP Rating	A
Mounting	Wall-mounted
Boiler Type	Combi
Type	Condensing
Fuel	Natural Gas
Warranty	5 years
Efficiency	89.3%
Dimensions	720mm x 440mm x 338mm