Overview
The S.7 error on a Vaillant EcoTEC (pump overrun) means the boiler has detected the central heating pump running as part of a pump overrun routine. Pump overrun is a normal function on many combi and system boilers: after the burner stops the pump continues to circulate water for a short period (typically around 5–10 minutes) to remove residual heat from the heat exchanger and prevent local boiling and damage. If the S.7 message appears only briefly after you have used the heating or hot water and clears after several minutes, it is generally not serious and is normal operation. If the S.7 condition is persistent (the pump keeps running for long periods with no recent demand) or the boiler never reaches target flow temperatures, this indicates a fault: common causes include a stuck or incorrectly wired pump, faulty timer/programmer or room thermostat, a stuck or faulty motorised valve/diverter valve, wiring faults, or a defective control PCB or sensor. A persistent S.7 can waste energy, cause unnecessary pump wear, and indicate an underlying electrical or component fault that needs professional attention. Homeowners can carry out basic checks and resets, but any work involving gas, internal electrical wiring, replacing the pump, motorised valves, PCB or internal components should be left to a Gas Safe registered engineer. If you smell gas, see internal water leaks, or the boiler is not operating safely, isolate the appliance and call a qualified engineer or emergency services immediately.
Possible Cause: Heating mode – pump overrun error
Troubleshooting Steps
Safety precautions:
1) If you smell gas, evacuate the property, turn off the gas at the meter if safe to do so, and call the gas emergency number immediately. Do not attempt repairs.
2) If you see water leaking from the boiler or standing inside the casing, switch off the electricity supply to the boiler at the isolator and the mains and call a Gas Safe engineer—do not operate the boiler.
3) Do not remove sealed covers, burn, or attempt internal electrical or gas repairs yourself. Only visual checks and non-invasive tests are suitable for homeowners.
Initial checks homeowners can do:
1) Note when the S.7 appears. Does it show only after you run hot water or the heating and then clear after 5–10 minutes? If yes, that is normal pump overrun behavior.
2) Observe the boiler display and symbols: check whether the pump symbol and gas symbol remain lit constantly or only during/after a demand.
3) Check the programmer/timer and room thermostat settings to ensure the heating/hot water is not being held on inadvertently (wrong schedule, frost mode, or manual override).
4) Check central heating pressure on the boiler gauge. Typical cold system pressure is 1–1.5 bar. Very low pressure can affect operation; if pressure is low, you can top up following the boiler manual instructions (if you are comfortable) but do not overfill.
5) Listen for pump noise and feel pipes (carefully) after turning demand off to see if the pump is still running. Record timing: how long does it run before stopping?
6) Bleed one or two radiators to remove trapped air if you hear gurgling or cold spots—air can cause flow/temperature issues.
Specific diagnostic checks and steps you can try:
1) Reset the boiler: switch the boiler off at the isolator, wait 30–60 seconds, then turn back on and see if the S.7 clears. Note any changes.
2) Reproduce the sequence: call for heating or hot water, then cancel demand and time how long the pump runs. Normal = around 5–10 minutes. If it runs much longer (hours) without demand, there is a fault.
3) Check external controls visually: ensure the room thermostat is set to a lower temperature than the room (so it can call off) and the programmer is not in permanent demand. Do not remove covers or touch live wiring—only visual inspection.
4) If you have motorised zone valves, check whether the valve lever/position indicators (if visible) appear to be stuck in the heat-on position. A stuck valve or failing motor can keep the pump running.
5) If the boiler’s heating flow temperature never reaches the set target, note the flow temperature and times—this can indicate a stuck diverter valve, faulty flow sensor (NTC), or faulty burner control and should be reported to an engineer.
When to call a professional:
1) If S.7 persists continuously (pump keeps running for long periods with no recent demand) after the basic checks and reset.
2) If you find water inside the boiler casing, visible leaks, or any signs of internal condensation/water ingress—switch off power and call a Gas Safe engineer.
3) If you are not comfortable topping up system pressure, bleeding radiators, or performing the checks above.
4) If visual checks indicate wiring issues (loose or damaged external wires) or if a newly fitted pump started the problem—call the installer or a Gas Safe engineer for safe electrical diagnostics.
What the engineer is likely to check and do (for your information):
1) Confirm the fault sequence on diagnostic menus and record error history.
2) Check programmer/thermostat wiring and operation, test zone valves/diverter valve movement, and inspect the pump wiring and operation.
3) Test sensors (flow/return NTCs), the control PCB and relays, and replace faulty components (pump, motorised valve, PCB) if necessary.
4) Repair any internal leaks or signs of water ingress and test the appliance after repair.
Notes for the engineer call:
1) Record the boiler model (Vaillant EcoTEC 65 kW), the exact error code S.7, when it appears, whether it clears after 5–10 minutes, any recent work on the boiler, and any visible water or unusual behavior. This helps the engineer diagnose more quickly.
2) Only use a Gas Safe registered engineer for diagnosis and repairs involving gas, internal electrical components or replacement of pumps, valves or PCBs.
If at any point the boiler behaves unsafely, or you are unsure, switch off the boiler and call a qualified Gas Safe engineer. Do not attempt internal repairs yourself.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Vaillant EcoTEC 65kW.