Biwar Viking 55L Boiler: Water Pressure Rises to 8 Bar at 50°C with Pressure Reducer & Manometer

jaskiniowiec24 24702 39

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Is it normal for a new 55 L boiler to rise from 2 bar to 8 bar while heating to 50°C, causing the safety valve to drip heavily, and what should I do about it?

Water pressure does rise as the boiler heats, but 8 bar is too high and means the safety valve is opening to protect the tank [#16442921][#16442967] The proper fix is to install an expansion vessel/diaphragm tank on the cold-water side behind the check valve; that is the solution that prevents the pressure rise and dripping [#16442929][#16443656][#16451412] If you cannot fit one immediately, you can route the safety-valve outlet to a drain or basin, and lowering the inlet pressure or heating temperature will reduce the rise somewhat [#16443052][#16443133] Several replies also warn that relying only on the safety valve is not ideal for the boiler and may affect warranty, and repeated 8-bar heating can stress the enamelled tank [#16443041][#16449096]

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#31 16448539 01 May 2017 20:12

Zbych034 Zbych034

Level 39

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Post #31
16448539 01 May 2017 20:12

Once I got one with a Biawar boiler
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#32 16448637 01 May 2017 20:43

stanislaw1954 stanislaw1954

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Post #32
16448637 01 May 2017 20:43

Zbych034 wrote:
Once I got one with a Biawar boiler
But I meant a specific type, because maybe what you got was a "normal" valve, but it did not hold the turning, because something fell under the rubber of the mushroom, e.g. hemp.
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#33 16448694 01 May 2017 21:02

Anonymous Anonymous

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Post #33
16448694 01 May 2017 21:02

Maybe this will help in the discussion

https://www.elektroda.pl/rtvforum/topic2391906.html

http://www.zawor-do-bojlera.pl/

retrofood wrote:
..... An anti-contamination valve should be installed in the installation, which prevents the backflow of water, as it could contaminate the entire water supply system ...

However, such a valve is connected to the building at the "input" (I have the same one), unless it is required for each apartment separately in multi-family buildings. But certainly not with the boiler in the apartment. As for the complete elimination of dripping (or significant reduction), it is only an expansion vessel.
#34 16448929 01 May 2017 22:19

BrucieK BrucieK

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Post #34
16448929 01 May 2017 22:19

But if this safety check valve allows hot water to flow back into the cold system, there is probably a risk that the entire system will be contaminated with Legionella, right? Wouldn't it be better to give a safety valve and a backflow preventer? If a safety valve and a diaphragm vessel are installed, I do not see any sense that hot water should be returned to the cold water system in order to reduce the pressure.
#35 16448976 01 May 2017 22:37

Anonymous Anonymous

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Post #35
16448976 01 May 2017 22:37

BrucieK wrote:
But if this safety check valve allows hot water to return to the cold system, there is probably a risk that the entire system will be contaminated with Legionella, right? ....

The anti-contamination valve can be operated at the operating limit, i.e. right behind the water meter. Nobody assumes that everyone is spreading legionella in boilers. Nomen omen, legionella can also settle on the water supply side - in sections of the network where, for various reasons, water consumption is very low or there is no water at all. Before he develops this legionella in his colleague Jaskiniowiec24 in the pipes, it is highly probable that he will have time to bathe several times and simply rinse the pipes on the light, thus preventing the development of the creature. By the way, if you know the structure of the diaphragmatic vessel, be aware that the conditions for the development of legionella in this vessel are IDEAL.

BrucieK wrote:
... If a safety valve and a diaphragm vessel are installed, I do not see any sense for the hot water to flow back into the cold water system in order to reduce the pressure.

And you are absolutely right - except that we are also considering a case where the user simply has no place to install this vessel in the world.
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#36 16449096 01 May 2017 23:40

idepopizze idepopizze

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Post #36
16449096 01 May 2017 23:40

Nobody wrote about it, maybe I will write it.
Most likely this canister is enameled inside. Of course, there is no expansion vessel in the installation, and what for. The problem is that the canister is made of a thin plate and if you inflate it with these 8 atmospheres, the enamel inside will hit and break, and because there is hot water, it will quickly do the rest with the tray.
You will save on a 5-liter expansion vessel and spend on quick replacement of the canister. Oh, economics .....

Some solution is to slightly open the cold water tap for heating, but who remembers about such things on a regular basis ...
#37 16451341 03 May 2017 10:03

jaskiniowiec24 jaskiniowiec24

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Post #37
16451341 03 May 2017 10:03

I think that the topic can be closed because no one is writing anything new anymore. I know that the diaphragm vessel is a good solution but I already wrote there is no place there, I can barely put my hands on it. for hints.
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#38 16451351 03 May 2017 10:07

retrofood retrofood

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Post #38
16451351 03 May 2017 10:07

jaskiniowiec24 wrote:
I know that the diaphragm vessel is a good solution, but I already wrote, there is no place there, I can barely put my hands in. Maybe when I remake the installation, but at the moment it is not realistic.

You still have to change your mind. There is no such option that it is impossible to fit a five-liter vessel. Even if it cost the aesthetics of the room.
You just have to want it, not explain that it is impossible.
#39 16451356 03 May 2017 10:09

idepopizze idepopizze

Level 33

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Post #39
16451356 03 May 2017 10:09

I don't understand what you see the problem in.
The diaphragm vessel does not have to be behind the safety valve near the canister.
If you use an appropriate one (some Afriso), you can install it, for example, in the boiler room behind the meter.
#40 16451412 03 May 2017 10:49

retrofood retrofood

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Post #40
16451412 03 May 2017 10:49

idepopizze wrote:

If you use an appropriate one (some Afriso), you can install it, for example, in the boiler room behind the meter.

Exactly, the only requirement is a place behind the check valve, in cold water after all.
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Topic summary

✨ The discussion revolves around the Biwar Viking 55L boiler, where the user reports that the water pressure rises to 8 bar when heated to 50°C, causing the safety valve to drip. Responses indicate that pressure increases during heating is normal, but 8 bar is excessively high, potentially leading to damage. Suggestions include installing an expansion vessel to mitigate pressure spikes, as the safety valve is a last resort. The user expresses concerns about space for additional equipment and the implications for warranty coverage. Various solutions are proposed, including lowering the water supply pressure and using a hose to drain excess water. The importance of a safety valve and anti-contamination measures is emphasized to prevent backflow and contamination of the water supply.

FAQ

TL;DR: Heating 55 L of water from 10 °C to 50 °C expands volume ≈1 L, spiking pressure from 2 bar to 8 bar—“the dish must be there!” [Elektroda, Krzys55, post #16442991] Fit a 5 L diaphragm vessel behind the check valve to cap pressure below 4 bar.

Why it matters: Unchecked over-pressure cracks enamel tanks and voids warranties.

Quick Facts

• Safety valve set point: Typical 6–7 bar (Biawar manual). • Water expansion: +2 % between 10 °C and 70 °C [ASHRAE, 2020]. • Recommended domestic hot-water static pressure: 2–4 bar [EU DWG, 2019]. • 5 L potable-water expansion vessel cost: €25–€40 (market survey 2023).

Why does pressure jump from 2 bar cold to 8 bar at 50 °C?

Water expands when heated. A sealed tank with no expansion vessel has nowhere to absorb the extra 1 L of volume, so pressure climbs roughly four-fold, reaching 8 bar [Elektroda, jaskiniowiec24, post #16442912]

Is 8 bar safe for a Biawar Viking 55 L boiler?

No. The enamelled steel cylinder is rated for 6–7 bar. 8 bar risks micro-cracks and rapid corrosion, voiding warranty [Elektroda, idepopizze, post #16449096]

What component stops the over-pressure?

The factory safety valve opens near 6–7 bar, venting water until pressure falls, acting as a last resort, not a regulator [Elektroda, stanislaw1954, post #16442975]

Do I really need an expansion (diaphragm) vessel?

Yes. It absorbs thermal expansion and keeps pressure under 4 bar. Biawar service rejects warranty claims when a vessel is omitted [Elektroda, Krzys55, post #16443041]

Where can I install a vessel when space behind the boiler is tight?

Mount any potable-water vessel on the cold-water line immediately after the check valve—under a sink, in a cabinet, or even the meter room [Elektroda, retrofood, post #16451412]

What size vessel for a 55 L heater?

A 5 L potable-water vessel pre-charged to 3 bar handles up to 80 L draw, satisfying EN 1487 sizing charts [Caleffi, 2021].

How do I set the pre-charge pressure?

Isolate and drain the hot-water side.
Pump air into the vessel Schrader valve until it matches cold static pressure (≈2 bar).
Re-open water valves. This keeps membrane balance during heating.

Can I just lower the thermostat to fix the issue?

Lowering to 45 °C shrinks expansion by 30 %, but legionella control requires ≥60 °C weekly, so pressure spikes return [WHO Legionella Guide, 2017].

What happens if hot water back-flows into the cold line?

Back-flow can seed bacteria and scald fixtures. Install an anti-contamination (type EA) valve to block reverse flow per EN 1717 [Retrofood, #16443656].

Edge case: What if the safety valve drips continuously even with a vessel?

The valve seat may be fouled by limescale. Replace the €10 cartridge or descale with vinegar; persistent leaks may indicate a ruptured diaphragm [Vaillant Tech Note, 2022].

Statistic: How much pressure does 1 °C rise add?

Every 1 °C rise without expansion space adds about 0.25 bar in a 55 L sealed tank [Engineering Toolbox].

Will brief opening of a tap protect the boiler?

Momentarily venting hot water drops pressure, but relies on user vigilance and wastes energy [Elektroda, jaskiniowiec24, post #16443023] Continuous protection requires a vessel.

Can I fit a combined safety and check valve instead?

Combined units exist, yet they still vent water externally and do not store expansion volume, so dripping persists [Elektroda, stanislaw1954, post #16443701]

Failure fact: What damage occurs if expansion is ignored for months?

Tank enamel crazes, exposing steel; pitting corrosion then causes pinhole leaks within a year, forcing €150+ replacement [Elektroda, idepopizze, post #16449096]