Vaillant turboTEC, Saunier Duval, Protherm Combi Boiler Air Pressure Switch 80/68 Pa – Huba 605.99E27, 0020041905

The Huba Control 605.99E27 air pressure switch is the safety component that monitors the flue draft in room-sealed combi boilers. It does not close its contact until the fan is running and has created sufficient vacuum in the flue line; the PCB does not ignite the burner without this confirmation. This is the part that prevents the appliance from operating with a blocked flue or a stopped fan.

The switching value is 80/68 Pa. The production code on the body is 60010102, and the original Huba equivalent on the Vaillant Group side is 605.99561.

What Does 80/68 Pa Mean?

• 80 Pa — upper switching point. When the fan vacuum reaches this value, the contact closes and the PCB receives the ignition confirmation.
• 68 Pa — lower point. If the vacuum drops below this value, the contact opens and the boiler shuts off the gas.
• The 12 Pa difference between them (hysteresis) is intentional. It prevents the contact from constantly opening and closing in wind and flue fluctuations, i.e. the appliance repeatedly locking out and resetting.

The switching point is set only at the factory; no adjustment can be made on the part. For this reason, a pressure switch with a "close" Pa value will not do the job.

🚨 Before Ordering: Always Read the Pa Value

All Pa steps of the Huba 605 series look exactly the same from the outside — body size, Ø6.2 mm hose nozzles and 3 faston terminals are the same on all of them. So a wrong value fits mechanically but the appliance does not work. Order by looking at the Pa value on the body of the removed part, not at the photo.

The values most often confused with this product:

• 85/70 Pa — ECA Calora and ECA Proteus use this value, not 80/68. This part does not fit them.
• 84/72 Pa — used in ECA models with DICOM boards. Only 4 Pa difference, same body.
• 60/50 Pa — the value of the Ariston Clas / Genus / Egis group.
• 74/64 Pa — Buderus Logamax U072.
• 90/70 · 105/90 · 110/98 Pa — higher steps. If one of these is fitted, the fan runs but the vacuum cannot reach the threshold, the boiler never ignites and constantly shows a flue fault.

Consequences of a Wrong Pa Value

• If a higher value is fitted, the fan cannot produce that vacuum and the contact never closes: the fan runs, there is no ignition, and the appliance goes into flue safety lockout.
• If a lower value is fitted, the safety margin is lost. Even with a partially blocked flue, the contact stays closed and the boiler continues to operate — there is a risk of flue gas leaking into the room. The safety function, which is the part's only job, is disabled.

Compatible Models

🪤 Note on the Vaillant side: this part belongs only to the turboTEC (room-sealed/fan-assisted) series. It is not used in ecoTEC (condensing) and atmoTEC (open-flue) models.

🪤 Note on the ECA side: in ECA's own spare parts list, code 7006901402 appears with a different Huba order number (605.99675) and no Pa value is given on that line. ECA Calora and Proteus use 85/70 Pa, models with DICOM boards use 84/72 Pa. Before ordering for your ECA appliance, read the Pa value on the removed part; if it does not say 80/68, this part does not fit.

Failure Symptoms and Error Codes

• Fan runs but no ignition. The most typical symptom — the PCB cannot receive the confirmation signal from the pressure switch.
• Intermittent lockout and reset. The contacts may be oxidized or stuck.
• "Clicking" from the relay and flickering flame. The vacuum is at the limit value, the contact is unstable.
• Fault in windy weather, no problem in calm weather. This means the diaphragm is fatigued.

🪤 The F5 code on the ECA Proteus Plus Blue also indicates the air pressure sensor, but that appliance uses 85/70 Pa — do not buy this part just because you see F5.

How Is It Tested on Site?

First the hoses are checked: cracks, hardening, soot or condensate blockage, looseness at the push-on points. A blockage at the flue terminal gives the same symptom. If the hoses are sound, the pressure switch is measured:

1. The multimeter is set to continuity (audible) or ohms.
2. With the fan stopped, the probes are held between the common terminal and the open contact — there should be no sound.
3. Gently suck by mouth on the hose nozzle (do not blow) — a "click" should be heard from inside.
4. At the same time the multimeter should beep and the resistance should read close to zero. When the suction is released, the sound should stop immediately.

Result: if there is no "click" at all, the diaphragm is torn. If there is a "click" but the multimeter does not beep, the contacts are burnt. In both cases the part is replaced.

🚨 Do not apply compressed air from a compressor or blow hard — this permanently tears the diaphragm. The test is done only by mouth, with gentle suction.

P1 and P2 Ports — Hoses Must Not Be Reversed

• P1 — the higher pressure (or lower vacuum) side; the atmosphere/reference port on the boiler.
• P2 — the lower pressure (higher vacuum) side; connected to the suction side of the fan, the negative port of the venturi.

If the vacuum hose is mistakenly connected to P1, the diaphragm is pushed in the opposite direction and the contact never pulls in; the appliance does not work. There is no mechanical damage, but this is the most common cause of cases thought to be "the new part arrived faulty". Mark the hoses before removal and fit the pressure switch in its original mounting orientation.

Technical Specifications

Technical document: Huba Control 605 series datasheet (PDF, English)