On my Carver heater in my caravan I had to replace the cold water inlet fitting on the hot water tank. This fitting incorporates a non return valve to prevent hot water backing up in to the cold water feed. Mine was leaking but I suspect the problem with yours is the valve is not opening fully if at all, hence the spurt of water. This is only a guess but if the feed to the heater is TEE'd off the cold feed to taps then this could be it, it's worth checking but like all, a bugger to get at no doubt, which I found on my caravan when on holiday couldn't take unit out had to do a 'Nose bleed' (almost stand on my head)
hope this helps.
Bob
May 2012
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