Noisy hot water pipes/system

[staithes14]

Hi.

Our hot water is an old fashioned cylinder (1st floor airing cupboard) supplied by a boiler down on the ground floor.

It comes on at 6am, followed by the central heating which comes on at 6.30.

This morning I was woken up by the noise of the HW coming on. There was a roaring, rushing, sort of 'fizzy' noise in the pipes, seemingly from somewhere above the cylinder, though I couldn't pinpoint it exactly.

It sounded like the sort of noise the garden hose makes, or like a mini tube train. It'd been doing this a bit recently but was louder than ever this morning. It woke me up and there are two walls separating me from it!

Strange thing I've noticed is that as soon as the CH kicks in, half an hour later, the noise dies away, leaving only the hum of the pump. As the noise dies away, there are some trickling sounds coming I think from Rad number 1 (our bedroom). I tried bleeding this but there's no air coming out.

I guess this must be to do with air but can anyone identify the specific problem?

Incidentally, the CH and HW seem to work fine. HW cylinder 'stat is set to 65C, boiler 'stat is set to full at the moment.

 

[staithes14]

Any ideas on this? I'd like to know if it's something I can fix before it wakes me up tomorrow.

 

[staithes14]

It's still doing it. I can hear it roaring away upstairs now. When the cold weather is over and we don't use the central heating it'll be every day (it doesn't make the noise when the heating comes on (maybe something to do with the diverter valve?)

 

[TheGasMan26]

Sound's like your HW is "pumping over", feel your rads, if theyv got cold spots in the middle then its likely you've got sludge in your "calorifier"(this is the coil within HW cylinder that allows the system water to heat your HW without touching it, so basically when it comes on & the sludge has settled all night theres to much resistance so it pumps over into the F&E(feed & expansion), tank in loft, after a while & pressure onto hw is split between rads it stops,
Best way to check for sure is get in loft when u hear the whoosing & look at the pipe that curves over the small tank & points downwards into it, then see if water shoots out of this, carefull itl be hot, also check this pipe isn't submerged. This is your "expansion" pipe, if this is the case then you will need to clear the coil somehow, ideally a powerflush but there are cheaper methods if u don't wanna spend loads.
Another possibilty is the coil is broke meaning the system water is pumping into hw cylinder then up the hw expansion pipe.
You can easily tell which one it is, if its pumping over into small(F&E) tank your coil is blocked, if its big tank(CWSC) your coil is broke & your hw will get contaminated.