Symptoms
- Rumbling, gurgling, or banging sound from the boiler when heating
- Sound similar to a kettle about to boil
- May worsen over weeks or months
Likely causes
- CommonLimescale buildup on the heat exchangerIn hard-water areas, minerals coat the exchanger and cause localized overheating and noise.
- CommonSludge buildup in the system from corrosionRust and debris circulating in the water restrict flow and cause hot spots.
- PossibleLow water flow through the heat exchangerA partially blocked pump or filter reduces flow enough to cause localized boiling sounds.
- PossibleTrapped air combined with scaleAir pockets can worsen the noise from scale-related hot spots.
What to do
- Note when the noise happens (right at startup, throughout the cycle) and how long it's been going on.
- Check the system's inline filter (if present) isn't visibly clogged; some are user-serviceable.
- Don't ignore ongoing kettling; ask about scheduling a professional flush before it causes a breakdown.
- Avoid using unproven descaling chemicals poured directly into the system without professional guidance.
- Reduce future scale buildup by asking a technician about a scale-reducing filter if you're in a hard-water area.
- Have a professional power-flush the system to clear scale and sludge from the heat exchanger and pipes.
When to call a pro
Call a heating technician to power-flush the system; kettling from scale or sludge can damage the heat exchanger if left unaddressed.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.