In the following article, we will explain in general what a check valve is and what function it serves in our installation. A handful of basic information.
The diagram shows the construction of a check valve with the direction of water flow indicated.
As depicted in the above diagram, the check valve in a central heating system operates by utilizing a design that allows water flow in one direction while blocking flow in the opposite direction.
Through the construction of the CH check valve, it can open under the pressure of the fluid to facilitate flow (in the desired direction), while simultaneously preventing valve opening in the opposite direction. We are aware that the schematic representation of the CH check valve provided is highly simplified, as check valves come in various designs and constructions. However, the principle of preventing water backflow remains consistent and relies on leveraging basic principles of physics, specifically the pressure mechanism induced by the water.
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While blocking reverse water flow is the primary function, the installation of a check valve serves more than just that purpose. In reality, in many CH systems without check valves, circulating pumps are subject to faster wear and tear. Therefore, the check valve can be considered an addition that positively impacts other elements of the installation and their longevity. A small check valve may seem insignificant, but it helps protect the money we've invested in heating.
✅ It's not to say that a CH pump shouldn't work without a check valve, but it's believed that in a system with a check valve, the pump should have a longer lifespan as it's less prone to failure (since it doesn't have to work against the backflow pressure of the medium). We all understand the implications of a circulating pump failure during winter, and none of us wish for that.
Unfortunately, water backflow can indeed affect the distribution of flow adequately across different circuits. This issue is more common in extensive installations and multi-story buildings, but it can also occur in single-story homes without separate heating circuits. Backflowing water leads to pressure loss in certain parts of the system, resulting in underheated areas where an adequate amount of hot water does not reach.
✅ In extreme cases, such a circuit should be divided into two smaller systems (each with its own circulating pump). Hydraulic low loss headers for CH systems are used for this purpose, as well as plate heat exchangers if the system needs to be completely divided into two isolated parts. However, often instead of investing in deviced as heat exchangers or low loss headers (here you'll learn more about low loss headers), simply installing a basic check valve is sufficient, which by the way should be included during system installation or servicing.
✅ Our information here is general and should be seen as indicative. The placement of a check valve in an installation should be determined by a professional who has seen and understands the specific installation.
An important consideration is the protection of devices that are components of the heating system. For example, it's recommended to install a check valve near water pumps, especially if the water comes from a private well. In this case, placing the valve between the water pump and the circulation pump can protect the water pump from potential backflow, which can be very beneficial for its technical efficiency, especially over years of operation. Additionally, a check valve in such a location can play a positive role in moments of pump failure (or lack of power to the pump, assuming there are no backup power sources). A warm system can largely operate via gravity, but in this case, the check valve will significantly support this operation. Therefore, in case of pump failure, the heating system can still largely operate via gravity, maintaining the temperature in the home.
The check valve is often present as a component of central heating pump groups, frequently on the cold side. Its purpose is to assist the operation of this specific water circuit before returning to the boiler, to avoid water stagnation in the boiler and overheating of the system. In the following pictures, although not visible, it is located under the blue thermometer, just before the manual shut-off valve.
Mixing pump group NORDIC TEC containing a check valve under the blue thermometer (cold side). The group includes a three-way mixing valve.
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