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- Hydronic heating
Underfloor heating maintenance: a step-by-step guide to flushing the system
The importance of flushing underfloor heating systems
For various reasons, deposits or dirt may accumulate in the system and reduce the efficiency of underfloor heating. Such a build-up can cause the following problems:
- uneven heating: if the water flow in certain heating circuits is restricted, the system hydraulics change and individual circuits can no longer be heated sufficiently.
- longer reaction times: if the water flow rate is too low, the amount of energy that can be released is also reduced. This results in longer reaction times for the heating circuits.
- increased energy consumption: deposits and dirt in the system water also increase the pressure losses in the system. The circulation pump then has to work harder and therefore consumes more electricity.
- system failure(s): if sediment builds up, it can cause corrosion and damage to various system components, such as the manifolds, pumps or valves. This can lead to premature replacements or failure of the underfloor heating system.
Regular inspection is recommended anyway, but if you notice any of the signs above, it might make sense to flush the underfloor heating system. Whether or how often a system should be flushed depends on various factors. In Germany and Austria, for example, there are standards and guidelines for the quality of system water. These include specifications for water hardness, pH value, electrical conductivity and limit values for various water components. This helps to ensure that the system functions optimally and that its overall service life is extended.
Safety first
As heating systems are very complex, flushing should always be carried out by a specialist company. Before you start flushing an hydronic underfloor heating system, it’s vital to take a few safety precautions. First of all, you need to turn the system’s power supply off to prevent any accidents or injuries. Then it is best to wait at least 30 minutes. This will allow the system to cool down and consequently avoid the risk of burns from hot water. There will also be no problems with stress on the components from being suddenly exposed to cold rinsing water.
If it becomes absolutely necessary to use chemicals, it’s also important to wear gloves and eye protectors and carefully follow the instructions to ensure you’re using the chemicals as prescribed and in the right quantities. Also ensure the building is properly ventilated so that vapours from the chemicals can’t build up inside.
Underfloor heating flushing step by step
In many cases a flushing plan is provided. The plan should include all subsystems, system connections and switching stations. All valves, coils, hoses and other equipment that can cause pressure surges should also be clearly identified.
These steps are recommended for thorough flushing of an underfloor heating system:
1. Draining the underfloor heating system
Depending on whether a partial flushing of individual system parts or the entire heating system is required, the section to be flushed must be shut off and drained. Draining is carried out via the return line at the filling and draining devices provided for this purpose, at the lowest point of the system or the part of the system to be flushed. Once the system pressure has been reduced, a vent valve should be opened at the highest geodetic point of the system in order to drain the system more quickly.
2. Performing an initial cleaning
When the system or system section has been drained, the first flush can begin. To do this, the filling device needs to be connected to the water connection or a flushing device in the flow and immediately drained again via the return. The dirt is flushed out in this process. This first rinse is carried out with clear water.
It’s important to ensure that flushing always occurs via the flow in the direction of the return, for example to prevent damage to the flow meters. Depending on the system configuration, it may also be necessary to bridge components with small flow openings (fine regulating valves, etc.) or pumps before flushing so that the dirt doesn’t get stuck in these components and cause blockages.
Furthermore, all regulating valves (balancing valves, thermostatic valves, etc.) should be set to the highest flow value. The setting values of these regulating devices should be noted in order to facilitate subsequent hydraulic balancing. The quality of the drained water should be checked during flushing. The first flush is complete when the drained water is clear and free of impurities.
3. Additional rinsing processes
After the initial cleaning, it may be necessary to carry out further rinses. Moreover, in case of heavily soiled systems, it may be necessary to work with abrasive or chemical additives. There are also special flushing devices that work with pulsed water flows. However, this work should always be carried out by specialised companies.
4. Refilling the system
After flushing, the valves should be checked for free movement and flow and cleaned if necessary. Of course, this also applies to filters, sludge separators, etc.
The system can then be refilled. Depending on the country, there are different requirements for the quality of the new filling water. While in some countries there are no specifications and the system is filled with drinking water, in other countries, for example, strict specifications apply to the filling water. For example, VDI 2035 applies in Germany and Ö-Norm H 5195-1 in Austria.
As with draining, a bleed valve must also be opened at the highest point when filling in order to completely fill the system with water. Furthermore, we advise to always keep an eye on the system pressure when refilling. A guide value for the system pressure at the lowest point of the system is the height of the system (geodetic height) plus an additional 0.3-0.5 bar. If, for example, the height difference from the lowest to the highest point of the system is 10 metres, the system operating pressure should be approximately 1.3 to 1.5 bar.
5. Hydronic balancing of the underfloor heating system
If the settings of control valves, pumps, etc. have been changed, these must be reset to the old values or a complete hydronic balancing must be carried out after recalculation of the system.
Only if the system is correctly balanced will each heating circuit receive exactly the amount of water it needs to cover the heating load. Moreover, a balanced system ensures fast and even heating as well as greater control accuracy, which in turn leads to better control quality and lower energy consumption.
Read more about the role of manifolds and flow meters in achieving a balanced system
6. Functional heating
When all the previous steps have been completed, a function test - a test run, so to speak - of the system is carried out to ensure that everything is working, that all parts of the system are supplied with the calculated amount of water and that each heating circuit actually heats up.
It may be necessary to ‘re-bleed’ the system after a certain period of time (approx. 1-4 weeks), when the air in the water has separated as a result of the system water heating up and/or any air pockets have been flushed out.
The steps above can also be applied to a radiator heating system as the procedure is quite similar to that of underfloor heating flushing.
Conclusion
A well-functioning underfloor heating system is very energy-efficient and offers high levels of indoor climate comfort. However, to ensure optimal functioning regular checks and, if necessary, maintenance are required. Should you have any further questions about flushing or other heating system maintenance procedures, please don’t hesitate to reach out to our experts. We will be happy to assist you with tailored advice.