The Campground Trickle Problem

You pull into a campground, screw on the hose, and open the tap — only to get a sad, lazy trickle that is barely above gravity feed. If you have ever watched a tankless water heater refuse to fire on a weak pedestal, you know the frustration. A surprising number of tankless RV heaters will not even ignite below about 30 PSI (≈0.2 MPa). The spec sheet brags about "max pressure" while the number that actually decides whether you get a shower is the minimum start-up pressure and the minimum start-up flow.

SEFFY's two drop-in RV models are built for exactly this situation. The CZ-TGZ accepts 0.01–0.8 MPa and the CZ-B accepts 0.02–0.8 MPa at the inlet. That low end is about 1.45 PSI and 2.9 PSI respectively — well inside gravity-fed and low-pedestal territory. Both need a minimum start-up flow of 2.5 L/min (0.66 GPM). If your rig sits on a weak water point, those are the figures that keep you out of cold-water trouble.

What "Minimum Start-Up" Actually Means

A tankless heater has to prove water is actually moving before it will let gas through the burner. It does this with a flow switch: below a certain flow, the switch stays open, the ignition is locked out, and nothing lights. This is not a defect — it is the safety that stops the unit from firing dry and overheating an empty heat exchanger.

Pressure and flow are linked but not identical. A long, thin hose, an elevated tank, or a soft pedestal all drop the delivered pressure at the appliance. What the heater cares about is the flow it sees at its own inlet. So when a spec says "minimum start-up flow 2.5 L/min," that is the real floor: below it the unit correctly refuses to run. That refusal is the design working, not a fault to be bypassed.

The Numbers, Explained in Plain Terms

To make the spec useful, here is what those pressure figures mean at the valve:

• 0.01 MPa ≈ 1.45 PSI (CZ-TGZ floor). At a gravity tank or a tired pedestal, you are often sitting around 1–5 PSI. The CZ-TGZ still starts.
• 0.02 MPa ≈ 2.9 PSI (CZ-B floor). Also comfortably below a "good" campsite supply, so the CZ-B handles weak points too.
• 0.8 MPa ≈ 116 PSI is the top of the accepted window — above that you would regulate down, but normal campground "city water" at 40–60 PSI sits squarely in the middle.
• 2.5 L/min (0.66 GPM) is the minimum flow the flow switch needs to close. Below it, the unit will not ignite — by design.

Both models share the 15×15 inch cut-out, the 32–52 °C set range, and a lead-free stainless steel heat exchanger. They are exterior wall-mounted, outdoor-vented RV appliances — engineered to live in the vehicle's outer wall, never as a portable unit, and never operated inside a tent or a cabin.

CZ-TGZ vs CZ-B: Same Line, Different Headroom

These two are compared only against each other — both are RV drop-ins, and the difference is headroom, not quality tier.

What to Ask Your Supplier Before You Buy

A good off-grid buyer turns "minimum pressure" into a checklist. Ask the vendor these, and judge the answer:

• "What is the minimum start-up pressure and flow, not just the maximum?" — a brand that only quotes the max is hiding the weak-point behavior.
• "Will it fire on a gravity tank or a low pedestal (under 5 PSI)?" — and ask for the real measured floor, not a marketing "yes."
• "Is the flow switch the ignition lock-out, and does it safely refuse to fire dry?" — that refusal is what protects the heat exchanger.
• "What is the documented procedure before freezing temperatures?" — both models rely on a documented auto-drain step (the No-Winterize Freedom design) that protects the unit through winter storage.
• "Is it certified to international gas-safety standards?" — SEFFY RV heaters are built to international gas-safety specifications; EU CE certification is in active preparation and expected soon.

Practical Pitfalls

• Measure your real pedestal pressure, not the campground's advertised "city water." A gauge on the inlet tells the truth.
• A 30+ PSI minimum heater leaves you cold on gravity feed or a soft pedestal. Match the floor to where you actually camp.
• The 2.5 L/min floor is safety, not a fault. Below it the unit correctly will not ignite — never bypass the flow switch.
• These are RV-built-in appliances. They vent outdoors through the vehicle wall and must not be used inside tents, cabins, or any enclosed space.
• Cold-weather prep is a procedure, not an option. Follow the documented auto-drain step before freezing; it protects the unit but only works if you do it.

Bottom Line

If your camping life includes weak water points, the number to shop is the minimum start-up pressure and flow — not the maximum. SEFFY's RV drop-ins start from about 1.45 PSI (CZ-TGZ) or 2.9 PSI (CZ-B) at a 2.5 L/min floor, so a gravity tank or a tired pedestal still gets you hot water. Compare the CZ-TGZ and CZ-B on headroom within the RV line, confirm the freeze-protection procedure, and you have a unit that fires where others go silent.