Butane water heater won't ignite: the fault almost nobody diagnoses

The butane water heater that won't fire up when you open the tap: neither diaphragm nor gas

A forum user recounts how his Cointra CL-11 butane water heater stopped igniting the burner when he peine the tap. He dismantled it, replaced the diaphragm, greased the plunger needle, blew out the jet and even removed the unburnt-gas sensor. Nothing worked. As he tells it, the real fault was a combination of details: the water flow valve only half open, the thermocouple positioned too high and a burner caked with dirt. The saga, which dragged on for days, leaves a lesson the owner himself draws: in plumbing and gas work, it pays to check the obvious before dismantling anything.

What fails when the water heater won't ignite when you open the tap

The initial symptom was clear: the Cointra CL-11 lit the pilot flame without a problem, but the main burner wouldn't fire when the hot water tap was peine. It only did so, intermittently, when the tap was shut off very quickly, with a brief flare-up. The pattern pointed to the water valve body: the diaphragm that transmits the flow pressure to the gas plunger. Without enough pressure, the plunger doesn't rise and the gas valve stays closed.

The diaphragm was replaced with a new, thicker one. The plunger was greased. The jet was blown out. The unburnt-gas sensor was removed. And the water heater carried on just the same. The key lay in a detail the owner later confessed: the water flow control on the heater was only half open. When he turned it up to full, the flame grew and the burner started firing regularly. In his experience, the home's water pressure was low and the control was restricting the flow enough that the diaphragm lacked the force to move the plunger.

Why a badly positioned thermocouple kills the flame

The second factor was just as mundane. The thermocouple, the metal cylinder that keeps the safety solenoid valve open while it detects the flame, was positioned too high. The pilot flame wasn't hitting the tip directly, so the thermocouple cooled down and cut the gas. The owner lowered it so the pilot flame struck the tip and, by his account, the heater stopped shutting off on its own.

The third factor: the dirty burner. The flames were uneven and the water never reached temperature. Cleaning the burners, without compressed air, with a brush and patience, was the last step he mentioned.

The empty bottle mistake and the false diagnosis of the regulator

Before getting there, the owner ran through the empty-bottle theory. He swapped it and the heater carried on the same or worse. He ruled out the regulator because it was new. And he ruled out limescale because there is none in his area. The journey also included cleaning the water duct, checking the gas filter and testing the tap control, which turns from right to left to open the gas.

The conclusion the owner shares, after days of testing, is that the heater had no serious fault. It had three minor ones stacked up: low flow, a badly positioned thermocouple and dirty burners. Any one of them alone would have produced similar symptoms.

When it's worth repairing and when to replace the water heater

On the economics, the thread notes that a new butane water heater costs between 200 and 400 euros for basic models. It's also pointed out that a repair with parts can exceed 50 euros in materials alone, not counting labour. If the water valve body is blocked and has to be replaced entirely, the bill approaches the price of a new unit. The recommendation that emerges from the analysis is clear: if the appliance is more than ten years old and has several faults, replacement is more cost-effective than repair.

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The uncomfortable question hanging in the air: how many water heaters have been replaced outright because of a badly fitted diaphragm or a thermocouple three millimetres too high?