Underfloor Heating Commissioning Procedure

Once installed, Polyplumb floor heating systems should be tested thoroughly to ensure they are working effectively, including initial filling of the system and system balancing.

Initial filling of system:

1. Close manifold isolating valves.

2. Connect a hose pipe to the manifold flow port via the drain off/filling point on the manifold. The other end of the hose should be connected to a mains cold water supply.

3. Connect a second hose to the return manifold and take it to a suitable discharge point such a drain or back inlet gully.

4. Open one of the blue decorator’s caps on top of the manifold and commence filling the system via the mains cold water supply. Once the water is running smoothly through the circuit and all of the air has been expelled, open the second blue cap and close the first. Repeat this process until all of the circuits have been filled and the system is free of air.

Close the drain / filling points and remove the hoses.

5. Connect a suitable pressure test pump to the flow manifold filling point and test the system to 6 Bar. Leave system under pressure for one hour to confirm the integrity of the installation. Once the pressure test is complete reduce the system pressure down to 3 Bar whilst the screed is applied.

Important note: Do not leave system under pressure during cold weather when there is a risk of freezing.

System balancing:

Once the system is up and running it will be necessary to balance the system in accordance with the design data as provided. This should be done using the following method.

1. Open the manifold isolating valves. Ensure that the boiler is operating correctly and that the correct temperature water is being provided at the manifold mixing valve. Please note that due to the design of the mixing valve it is necessary to provide water from the boiler at least 15ºC hotter that the required underfloor heating operating temperature.

For example; if the underfloor heating system has been designed to operate at a flow temperature of 50ºC, the boiler should be able to provide a primary flow temperature to the manifold mixing valve of 65ºC min. (Please note that for systems connected to a heat pump installation different criteria may apply. Please contact Polypipe Technical Support for further information.) Adjust the mixing valve temperature setting accordingly to match the precise manifold design requirement using the dial thermometers as supplied.

2. Ensure that the underfloor heating circulating pump is set to a suitable fixed head speed using the pump adjustment facility. This is particularly important for systems fitted with modulating pumps. Remove the blue caps from the manifold return rail (or actuators if already fitted) and using the radiator key supplied adjust the circuit/s to each room in accordance with the Polypipe design data. This is done by fitting the radiator key over the square fitting that protrudes from the top of the valve body. By turning the key clockwise the flow rate is decreased. To increase flow rate turn the key anticlockwise. Adjust each circuit until the flow meter on the manifold flow rail reads the required flow rate. Repeat the procedure for all circuits connected to the manifold. If a modulating pump is fitted return the pump to its modulating operation mode.

3. Refit the manifold actuators and check their correct operation to each circuit by operating the
appropriate room thermostats.

Pressure testing in sub zero temperatures Special precautions are necessary if the pressure testing is to take place in sub-zero temperatures. This applies particularly when using the screeded floor
heating system, where most of the pipe is encased in screed. Due to the contact between pipe and floor panel on screeded installations, where the screed does not completely surround the pipe, there may be points where strain is created on the pipe in freezing conditions, which is not normally present. Therefore, it is advisable to drain the floor heating system once testing and screeding has been completed.

System chlorination

Short term chlorination for disinfection of supply pipework and normal levels of chlorine in UK domestic water supplies will not have an adverse effect on Polyplumb. Polyplumb is not suitable, however, for systems that carry a high concentration of chlorine, ie supplies to swimming pools, etc.


If there is an excessive amount of air present the system will be noisy and the flow meters may appear to bounce up and down. If this happens, repeat the initial filling procedure until the system
is fully purged of air.

If the system has been left standing for a long period of time or if contaminants are present in the system water, the flow meters may appear discoloured or cease to work. If this is the case, turn off the manifold isolating valves and remove the manifold flow meter/s. Using a soft brush, gently wash under a tap until all of the debris has been removed. Check the manifold opening for any signs of contamination and flush the system if necessary. Refit manifold flow meters.

Should the damage to the flow meter/s be too great it/they should be replaced.

If the original system design data has been lost or is unavailable it is possible to adjust the manifold
flow rates using the simple rule of thumb method as described below:

As the maximum length of any single Polypipe underfloor heating circuit should not exceed 100m, we know that when installed in to a solid floor system using 100mm pipe spacings and allowing for minimum connection lengths, it is possible to cover approximately 10m2 of floor area. Given the maximum heat output achieveable from this type of system (100 watts per m2) we therefore know that a 10m2 area of floor can give out approximately 1kW of heat. In order to meet this requirement a flow rate setting of approximately 1.5 litres per minute will be required. Typical average flow rates assuming a 10ºC temperature drop across the manifold:

  • 50 watts per m2 = Flow rate setting 0.7 l/pm
  • 75 watts per m2 = Flow rate setting 1.0 l/pm
  • 100 watts per m2 = Flow rate setting 1.5 l/pm

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