Install underfloor heating manifold: Step-by-step guide 2026

Install a manifold for underfloor heating: Step-by-step guide 2026

Install a heating circuit distributor yourself – here's how to do it right. This guide will take you from distribution box installation, through pipe connection and bleeding, to pressure testing according to EN 14336. With a tool list, 8 concrete installation steps, and answers to the most common DIY questions.

⏱ 11 min read

8 assembly steps explained

Pressure test 6 bar correct

Preparation: Tools, Material & Mounting Position

Tools & Aids

→Pipe wrench or water pump pliers (for G 1" connections)
→PTFE thread seal tape (min. 12 layers)
→Hand pressure pump for pressure testing (0–6 bar, integrated manometer)
→Bleed key or flat-blade screwdriver for bleed valves
→Spirit level (for horizontal alignment of the manifold)
→Dowel & screws (M6, for distribution box wall mounting)

Prerequisites before assembly

→Set manifold position: max. 20 m from boiler/heat pump, central to all heating circuits — minimizes pipe lengths and pressure loss
→Is there a flow sensor in the supply pipe, or is one planned? (Mandatory for boiler control)
→All underfloor heating pipes laid and accessible? Only install after screed has been laid and dried
→Wall niche chiseled out for flush-mounted box or wall surface cleared for surface-mounted installation
→230V power supply within reach for actuators and room thermostat cable (if desired)

Common Errors & Warnings

The installation of the heating circuit distributor is the critical interface between the boiler/heat pump and the underfloor heating system. Errors here lead to water loss, pressure drop, and, in the worst case, damage to the screed.

Connection Diagram: Heating Circuit Distributor in the SystemTypical single-pipe system in a single-family home

Boiler / HPFlow 35–55 °C
Return 25–45 °C

FL DN 25
G 1"

Pump GroupDifferential pressure
control

→ Distributor

Heating Circuit DistributorFL top / RL bottom
Stainless steel DN 25

PE-RT
Ø 16–20 mm

Heating Circuits 1–nEach 8–16 m²
Pipes in screed

FL (red) top, RL (blue) bottom — Standard according to VDI 6000

Step-by-Step: The 8 Critical Installation Phases

Step	Activity	Standard / Value	Common Error
1 – Position	Install distributor box near exterior wall; minimize supply line length	VDI 6000: max. 10 m supply line	Too far from heating: unnecessary pressure losses
2 – Wall Mounting	Mount box with min. 4 anchors, 100 mm depth for inspection access	DIN 18380	Box too shallow: hoses kink
3 – FL / RL Connection	Flow (red) top, Return (blue) bottom; G-1" thread with min. 8 layers of PTFE tape	VDI 6000, G 1" EN ISO 228	Too little PTFE → micro-leak after weeks
4 – Heating Circuit Hoses	PE-RT Ø 16 mm with Eurocone screw connection; bending radius ≥ 8×d	EN ISO 15875	Sharp kinks at distributor outlets
5 – Filling	Fill each circuit individually, open vent at distributor; system must be bubble-free	Min. 1.5 bar filling pressure	Air bubbles remain → uneven heating
6 – Pressure Test	Increase pressure to 6 bar (cold test); hold for 24 h — no drop allowed	DIN EN 1264-4: 6 bar / 24 h	Only 2–4 bar tested → hidden leaks
7 – Protocol	Fill out pressure test protocol (date, initial pressure, final pressure, inspector)	DIN 18560: Document for screed	No protocol → warranty issues
8 – Balancing	Set flowmeter per circuit to target flow (l/h according to heat load calculation)	GModG § 60 (formerly GEG)	All circuits turned on equally → cold/warm unevenly

Pressure Test: Values, Protocol, and Common Errors

6 barCold Pressure Test
DIN EN 1264-4

24 hMinimum Holding Time
without pressure drop

0 barPermissible Pressure Loss
in 24 hours

After the pressure test, the water must not be drained — the pressure remains in the system until the screed installation is complete. The screed layer must receive the pressure test protocol, otherwise they may reject warranty claims for screed damage.

Important: Protocol Requirement in Germany

Pressure test protocol according to DIN 18560 is a mandatory document for the screed layer
Without protocol: no warranty from the screed company
Provide a copy to the construction diary and the building owner
For renovations (GModG § 60): retain protocol as proof of efficiency measure

The 6 Most Common Installation Errors and How to Avoid Them

Too Little PTFE Tape

At least 8 layers of PTFE sealing tape on the G-1" thread. For stainless steel distributors, always combine with hemp fiber plus PTFE for permanent sealing.

↔

Incorrect Flow/Return Direction

Flow (red, hot) strictly at the top, return (blue, cooler) at the bottom. Reversing leads to air problems and inefficient heat distribution.

Distributor Box Too Small

Minimum box dimensions: Width = distributor width + 10 cm, Depth = 10 cm (hose bending). Boxes that are too tight force hoses into impermissible bending radii.

Unvented Heating Circuits

Fill each circuit individually and completely vent through the bleed valve on the distributor. Residual air leads to cold spots and uneven heating.

Regional Peculiarities: Germany, Austria, Switzerland

In Germany, the Building Modernization Act (GModG) has been in effect since July 2026, replacing the former GEG. § 60 GModG mandates hydraulic balancing for all buildings with central heating supply — the pressure test and flowmeter setting at the distributor are thus a legal obligation for new installations and renovations. In Austria, OIB Guideline 6 applies, and in Switzerland, SIA 384.

→Step 1: Fit the distribution box into the wall recess, align it horizontally, and fasten it with wall plugs
→Step 2: Screw ball valves (flow at top / return at bottom) to manifold with PTFE sealing tape
→Step 3: Insert manifold into the box, snap in holders
→Step 4: Connect the underfloor heating pipes (flow and return) sequentially to the manifold connections - label the circuits!
→Step 5: Slowly fill the system with water via the ball valve, bleeding each circuit individually
→Step 6: Perform pressure test with manual pressure pump to 6 bar for 30 minutes — no pressure drop = sealed
→Step 7: Screw actuators (E30NC-230) onto all manifold outlets, route cables to room thermostats
→Step 8: Set flowmeter to target value (0.5–2.5 l/min per circuit depending on room size) and commission heating

Achtung – Fachmann empfohlen

Threaded connections without sufficient PTFE sealant tape (at least 12 layers) lead to slow leaks—especially at G 1" threaded connections.

Achtung – Fachmann empfohlen

Pressure test at 6 bar MUST be performed before closing the wall niche or before plastering — subsequent repairs are costly.

Frequent questions about heating circuit manifold installation

The installation of the manifold itself (mechanical installation) is permitted as a craft without the need for a master craftsman's license. The connection to the heating system (boiler side) should be carried out by a heating engineer if there is no specialist knowledge — especially with heat pumps. You can document the pressure test yourself. GEG § 60 (Hydraulic Balancing) does not require a specialist company but must be documented.

Experienced DIYers need approx. 2–3 hours for a 4–6 circuit manifold, including bleeding and pressure testing. Initial installation without prior knowledge: 4–5 hours. Most time-consuming step: assigning and labeling the underfloor heating pipes to the correct circuits (30–45 min.). A professional heating engineer needs approx. 1.5–2 hours, but typically charges for half a working day.

Filling Step-by-Step: 1. Close all circuits on the manifold except circuit 1. 2. Slowly open the ball valve, fill the circuit until water exits the vent without bubbles. 3. Close the vent. 4. Open the next circuit, repeat. 5. All circuits open: Set system pressure to 1.5–2 bar. Important: never fill quickly — trapped air leads to noise (gurgling) and uneven heating.

Pressure drop > 0.1 bar in 30 minutes indicates a leak. Procedure: Check all threaded connections on ball valves and manifold connections with leak detection spray. Most common cause: insufficiently wrapped PTFE sealing tape. Remedy: Loosen the fitting, rewrap the sealing tape (12+ layers), and retighten. For underfloor heating pipes themselves: leaks due to kinking or crushing usually occur during installation, not at the connection.

Upon initial startup: max. 25 °C flow temperature for 3 days (avoid screed burn-in phase — applies only to new construction). Then gradually increase to operating temperature. Operating temperature: heat pump 30–40 °C, gas heating 45–55 °C. For underfloor heating, nighttime setback max. 3–4 °C — too large a setback costs more energy than it saves, because the heating-up time becomes too long.

Labeling is not mandatory, but highly recommended – you'll be glad you did, at the latest when performing hydraulic balancing or troubleshooting. Standard: Metal plates or adhesive tape labels on the manifold, e.g., 'LR' (living room), 'BR' (bedroom), 'B1' (ground floor bathroom). Additionally: Photograph a sketch of the circuit layout and place it with the manifold plan in the building services folder.

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