Banging noise when hot water turned on

Dragonflew1010

This has been going on for nearly a year now or more. It doesn't start banging until the water turns hot (takes around 20 seconds before it heats up) and stops as soon as the hot water tap is off. Consistent banging to a beat.

Sometimes after turning it off and on again, the hot water doesn't arrive until I turn the tap on more, after which is gushes a bit then returns to the normal flow.  

This only occurs with the sink downstairs, the bath upstairs is fine. 

And recently both the bath and sink have starting dripping even when fully closed. Hopefully not related but that's another story.

 

Lorian

Combi boiler or tank fed hot water?

Dragonflew1010

Lorian said:

Combi boiler or tank fed hot water?

Combi boiler

WIAWSNB

Dragonflew1010 said:

This has been going on for nearly a year now or more. It doesn't start banging until the water turns hot (takes around 20 seconds before it heats up) and stops as soon as the hot water tap is off. Consistent banging to a beat.
Sometimes after turning it off and on again, the hot water doesn't arrive until I turn the tap on more, after which is gushes a bit then returns to the normal flow. 
This only occurs with the sink downstairs, the bath upstairs is fine.
And recently both the bath and sink have starting dripping even when fully closed. Hopefully not related but that's another story.

Make and model? (not that i think it'll help...)

This banging - is it from pipes, or from the boiler itself?

The symptoms are a bit weird, and don't fit in with any single cause that I'm aware of.

'Banging' of any sort in a boiler usually suggests overheating, or perhaps a scaled-up heat exchanger. Possibly the kitchen tap has less flow - having a smaller spout - than the bath tap, so this allows more overheating of the DHW? Ie, it cannot shift the heated hot water fast enough, so the boiler overheats (which it shouldn't, of course...).

Can you adjust the DHW flow temp? What's it currently at? 

Lots of possibilities, but it would be stabbing in the dark; sticking diverter valve, faulty flow temp sensor, scaled-up exchangers (P2P or MainX), and goodness knows what else.

I fear there is no 'user' solution to this, unless turning down the flow temp helps?

glennevis

I get this when I run the bath's hot tap. I think it's due to the pipe running through the joists near the bath. The hole must have been a bit tight so it only happens when the hot water starts to come through because the pipe has expanded slightly.