My boiler makes an horendous noise its a Potterton promx 15 sl
What's your's? is it a Truma / Carver underseat mounted wall mounted or what?.
Meanwhile I'll assume it's a underseat Truma/carver may be the tanks holed or the water connection is slightly loose I had a Truma/carver leak and it was the water inlet connection valve split.
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Try fixfault.com to fix caravans/motorhomes.