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What is the function of the safety valve?

The heater safety valve incorporates a non-return valve that prevents water from being pushed back into the water main. Water dripping during heating is normal and indicates correct functioning of the safety valve. When water is heated, its volume increases by up to 3.5% of the heated volume. This means that for a volume of 120 liters, 4.2 liters should run out. The volume of dripped water may differ, depending on several factors (heated volume, temperature difference between and after heating, pressure in the water main).

If water drips outside heating, it can be due to one of the following problems

  • dirt or deposits in the valve can cause dripping; we recommend turning the valve or lever (Italian type) on top of the valve; this should be done preventively every three months.
  • at high inlet pressures above 4.8 bar, it is necessary to place a pressure regulator on the inlet pipe (we recommend reducing the inlet pressure to approx. 3 bar)
  • of course, the dripping can also be caused by a failure of the safety valve itself.

If water drips only during heating, put a tube on the sleeve and drain it. The water outlet must not be led upwards, it must not be longer than two meters and must be protected against freezing and pressing. However, a better solution is to install an expansion vessel between the water heater and the safety valve. The expansion vessel should have a volume of approximately 5% of the water heater vessel. Then there will be no wastage of water. In some countries, this solution is even mandatory.

Recommended minimum expansion vessel volumes by heater capacity

Heater capacity (l) 50 80 100 125 160 180 200 250 300 400 500 750 1000
Expansion tank capacity (l) 2,5 4 5 6 8 8 8 12 12 18 24 33 50


What is the use of a non-return valve for combined water heaters?

The non-return valve should be located at the inlet of the exchanger. Here it is necessary to pay attention to the aeration of the heat exchanger. If there is a lot of air in the water or you don’t have a strong enough pump, I would recommend placing the vent valve between the exchanger and the non-return valve. However, a non-return valve is not recommended for “gravity” systems as it increases the hydraulic resistance in the pipe.

The non-return valve closes when water stops flowing in the allowed direction (sometimes, a non-return valve that operates in different positions is used – has a spring). The non-return valve operates only in one position. It is a mechanical part, sold separately, like a shut-off valve.

How come hot water can smell?

This problem is more due to the water itself than heaters. Some waters (wells, untreated) contain large amounts of sulfate together with bacteria that reduce the sulfate. These bacteria, harmless to health, in stagnant waters, which have been deprived of oxygen, produce hydrogen sulfide gas (odor) and utilize hydrogen ion from anode the protection. The greater the activity of the anode (low water quality), the more the hydrogen ion and the more gas produced hydrogen sulfide. These bacteria cannot grow in the presence of atmospheric oxygen and therefore are not present in cold water sources. If the same water is heated, they will appear. In some cases, it helps to replace the anode with another one that has a different composition. If, however, this does not solve the problem, we recommend removing the anode, although this will reduce the life of the water heater.

I have the DKD OK 2A vertical water heater. With which type of heater (of the same parameters) of the current production program of your company can I replace it?

This product was replaced by the OKC 125 which is a combined water heater with a capacity of 125 liters. The dimensions of the hinges are identical (450 mm), but, unfortunately, the spacing of the outputs is now 440 mm, which is 100 mm more and the outlets are led to the back and not to the side. Our offer no longer includes a model with outlets on the side. Functionally, this heater is identical to the previous type.

How to drain water from a heater?

1) Turn off all electrical heating elements inside the heater!

2) Close the cold water supply to the heater(s),

3) open the how water valve (tap) somewhere in the associated pipeline (be careful with lever faucets – only hot water is to be opened). If you want to drain all the pipes of the hot water, open all related valves.

4) Place a sufficiently large container under the outlet of the heater drain valve, or bring the water into the drain!

5) Open the drain valve of the heater! The drain valve should be at the “T” junction, just before the cold water inlet of the heater (in stationary heaters, this is sometimes at a completely separate output at the bottom)

6) if you could not find the heater drain valve, drain the heater through a test (relief) valve that is part of the safety valve

7) after draining the heater completely, close all valves (taps) again!

Caution: When draining the heater for the winter, remember to drain the water system as well. If the heater is then without water for a longer period of time, it is recommended to rinse it before reuse.

How to clean the inside of a water heater?

After draining and opening the heater, you will see how much the exchanger is clogged with limescale. If the lime is soft, you should be able to rinse or remove it with a stream of water or with a cloth. If the lime is hard, we recommend removing it with a wooden object (carefully, avoid damaging the enamel at all costs). We recommend obtaining a new gasket under the flange and a magnesium anode with a service life of 2 years and to replace everything.

The amount of wear depends on the operation and water. Both can be sent cash-on-delivery.

Is it possible to use the TJ heating elements in stainless steel water heaters and storage tanks?

TJ heating elements are not designed for stainless steel tanks. These products are designed mainly for the use in the water heaters and storage tanks produced by Drazice.

Družstevní závody Dražice-strojírna s.r.o.
Dražice 69, 294 71 Benátky nad Jizerou
Czech Republic
Tel.: +420 326 370 911
E-mail: info@dzd.cz