Symptoms: When should the distributor be replaced?
Tools & Aids
- →Pipe wrench or water pump pliers (for G 1" connections)
- →PTFE thread seal tape (min. 12 layers)
- →Hand pump for pressure testing (0–6 bar, integrated pressure gauge)
- →Bleed key or flat-blade screwdriver for bleed valves
- →Spirit level (for horizontal alignment of the manifold)
- →Anchors & Screws (M6, for distribution box wall mounting)
Checklist before retrofitting
- →Determine manifold position: max. 20 m from boiler/heat pump, central to all heating circuits — minimizes pipe lengths and pressure loss
- →Flow sensor in the supply pipe present or planned? (Mandatory for boiler control)
- →All underfloor heating pipes laid and accessible? Only mount after screed installation and drying phase
- →Wall niche carved out for flush-mounted box, or wall surface cleared for surface-mounted installation
- →230V power within reach for actuators and room thermostat cables (if desired)
Retrofitting: Scenarios, Process, and Funding
The heating circuit distributor needs to be retrofitted when installing a new heat pump, expanding the heating system, or replacing a defective/outdated distributor. In Germany, this comes with significant funding opportunities – but also clear legal requirements.
When is retrofitting useful or necessary?
| Situation | Retrofit Need | Typical Costs (DIY) |
|---|---|---|
| Install heat pump | Yes – if old distributor is brass | €150–€280 (stainless steel set) |
| Expand underfloor heating by 2–4 circuits | Yes – larger distributor needed | €120–€250 (replacement) |
| Distributor leaking / defective | Yes – immediate action | €100–€200 (replacement same size) |
| No hydraulic balancing possible | Yes – if no flow meters are present | €80–€130 (distributor with flow meters) |
| Old plastic/chrome steel system | Recommended – during renovation | €150–€320 (complete set) |
| Retrofit actuators | No – distributor remains, actuators are added | €15–€35 per actuator |
Retrofitting in old buildings: Special features and common problems
Pipe connection compatibility
Older underfloor heating systems may use 3/4" connections instead of the G 1" standard. Reducers G 1" → 3/4" cost €3–€8 per connection and allow for universal connection.
Check water hardness
Before replacing, measure water hardness (pharmacy or test strips). Below 8.4 °dH: stainless steel is mandatory – brass leads to dezincification. Request a free test from your water supplier.
Sludge in the return flow
Old building underfloor heating systems often have sludge and oxide deposits. Before installing the new distributor: Flush each circuit individually with a flow velocity ≥ 0.5 m/s.
GModG § 60 for renovation
When replacing heating in Germany: hydraulic balancing is mandatory. A distributor with flow meters enables DIY balancing and saves €200–€500 in craftsman costs.
Replacement process: Old distributor out, new one in
Step-by-step: Distributor replacement
1. Shut offShut off flow + return
supply
supply
15 Min
drain
drain
2. Loosen circuitsUnscrew each circuit
individually
individually
Note
position
position
3. New distributorMount, PTFE
8 layers
8 layers
Connect
circuits
circuits
4. Fill & bleedCircuit by circuit,
6 bar pressure test
6 bar pressure test
Before loosening: Photograph the circuit layout! Room assignment (which circuit = which room) is essential for later balancing.
Retrofitting costs and funding opportunities
€150–€280DIY total costs
6-circuit stainless steel set
6-circuit stainless steel set
€500–€900Professional replacement
incl. material & balancing
incl. material & balancing
up to 80 %KfW 458 funding rate
with heat pump combination
with heat pump combination
Funding for distributor retrofitting: What's possible?
- KfW 458 (Federal Funding): Distributor as part of the underfloor heating system eligible for funding when installing a heat pump – up to 80% of total costs
- BAFA Heating Optimization: Hydraulic balancing according to gG method B – flat rate of 30% of costs up to a maximum of €600 per unit
- State Programs: Bavaria (BayernFonds), North Rhine-Westphalia (progres.nrw), Hamburg (IFB) have supplementary programs
- Austria: Sanierungsscheck (Renovation Check), federal state programs (e.g., Wien Wärme Bonus)
- Switzerland: Cantonal building program – cantonal energy expert advises
- →Step 1: Fit the distribution box into the wall recess, align it horizontally, and secure it with anchors.
- →Step 2: Screw ball valves (flow top / return bottom) to manifold using PTFE sealing tape
- →Step 3: Insert manifold into the box, engage retainers
- →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 all circuits individually
- →Step 6: Carry out pressure test with hand pressure pump at 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 the reference value (0.5–2.5 l/min per circuit depending on room size) and start up heating
Achtung – Fachmann empfohlen
Threaded connections without sufficient PTFE sealant tape (at least 12 layers) lead to creeping leaks — especially on G 1" threaded connections.
Achtung – Fachmann empfohlen
Pressure testing at 6 bar MUST be carried out before closing the wall niche or before plastering — subsequent repairs are costly.
Frequent Questions about Heating Circuit Manifold Installation
The installation of the distributor itself (mechanical installation) is permitted as a craft without the need for a master craftsman's certificate. 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 usually charges for half a working day.
Step-by-step filling: 1. Close all circuits on the manifold except circuit 1. 2. Slowly open the ball valve, fill the circuit until water emerges from the vent without bubbles. 3. Close the vent. 4. Open the next circuit, repeat. 5. With all circuits open: Set the 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 means: there is 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 screw connection, re-wrap the sealing tape (12+ layers), tighten again. Underfloor heating pipes themselves: leaks due to kinking or crushing usually occur during installation, not at the connection.
For initial commissioning: max. 25 °C flow temperature for 3 days (avoid screed curing phase – only applies to new builds). Then gradually increase to operating temperature. Operating temperature: heat pump 30–40 °C, gas heating 45–55 °C. For underfloor heating, night setback max. 3–4 °C – too sharp a reduction costs more energy than it saves, because the heat-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 tags or tape labels on the manifold, e.g., 'LR' (Living Room), 'BR' (Bedroom), 'B1' (Bathroom Ground Floor). Additionally: take a photo of the circuit layout sketch and place it with the manifold plan in the building services folder.
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