Navien
Navien Expansion Vessel 6L 30029043A
6-litre expansion vessel for Navien NCB300 and NCB500 combi boilers, part number 30029043A.
£174.01
£145.01 ex. VAT · VAT at 20%
Same-day dispatch
Ordered by 4pm Mon–Fri, 10:30am Sat.
30-day returns
Unused, in original packaging.
What it is
The Navien 6-litre expansion vessel, part number 30029043A, is a sealed diaphragm vessel fitted to Navien NCB300 and NCB500 combi boilers. It absorbs the volume increase of water as the heating circuit warms, limiting pressure rise across the system. It is a serviceable component within the boiler's hydraulic assembly.
Signs this part needs replacing
- System pressure climbs sharply as the boiler heats and falls back once it cools
- Pressure gauge reads high, with water discharging from the pressure relief valve
- Pressure drops repeatedly and the system needs frequent topping up
- Water or corrosion staining around the vessel connection
- Diaphragm failure, leaving the vessel waterlogged and without its pressure cushion
Before you order
- Confirm the boiler model and serial number against the fitment list
- Check the existing vessel is 6 litres and carries part number 30029043A
- Confirm access to the vessel and its connection point before starting work
No specification data held for this part.
| Make | Model / assembly | Reference | Years | Fitment |
|---|---|---|---|---|
| NAVIEN NCB300-28K COMBI - (Serial Number 3710) | — | — | — | |
| NAVIEN NCB300-28K COMBI - (Serial Number 3710) | — | — | — | |
| NAVIEN NCB300-37K COMBI - (Serial Number 3734) | — | — | — | |
| NAVIEN NCB300-37K COMBI - (Serial Number 3734) | — | — | — | |
| NAVIEN NCB300-41K COMBI - (Serial Number 3711) | — | — | — | |
| NAVIEN NCB300-41K COMBI - (Serial Number 3711) | — | — | — | |
| NAVIEN NCB500-1S+/32K COMBI - (Serial Number 3924) | — | — | — | |
| NAVIEN NCB500-1S+/32K COMBI - (Serial Number 3924) | — | — | — | |
| NAVIEN NCB500-2S+/41K COMBI - (Serial Number 3712) | — | — | — | |
| NAVIEN NCB500-2S+/41K COMBI - (Serial Number 3712) | — | — | — |
Showing 10 of 12 compatible appliances.
Documents & drawings
Everything we hold for this part. Where a document exists but we don't hold it, the technical team will source it from the manufacturer — usually the same working day.
NAVIEN appliance manual — NCB300-28K COMBI - (Serial Number 3710), NCB300-37K COMBI - (Serial Number 3734), NCB300-41K COMBI - (Serial Number 3711)
manualmanualNAVIEN appliance manual — NCB500-1S+/32K COMBI - (Serial Number 3924), NCB500-2S+/41K COMBI - (Serial Number 3712), NCB500-2S/37K COMBI - (Serial Number 3735)
manualNo technical questions yet for this part.
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