Hot water problem could be a faulty sensor. Probably the cause and the cheapest thing to try first, other possible faults could be gas pressures incorrectly set or plate heat exchange needs replacing.
The pipes may just need clipping and lagging, movement in the pipes can sometimes sound quite loud especially if they're just loose with no supports or clips. Also widening the notches in the joists slightly so the pipes aren't rubbing against the wood may help.
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