New combi central heating - noises!

[mth]

Hi all

I've just had a new external Firebird c20 installed for our heating and hot water.

This is the first time we've ever had central heating although the pipes were all put in the house 20 years ago when built (it was meant to have a log burner to do the heating but it was never installed).

Anyway, when the boiler is keeping itself warm overnight (with just hot water switched to on, i.e. no heating overnight), or when I first turn the boiler on if it's been off for a while, I get noise coming up the flow pipe for the central heating. I put my hand on the pipes to work out which pipe was 'vibrating' when it happened.

I would greatly appreciate some input

Thanks
Matt

 

[mth]

I've made some progress on this, but it's not fixed yet. Here's the situation now:

When it first comes on to fill/heat the heat exchanger in the morning (it's switched off overnight) it sounds like its sucking water out of my heating system and spitting it back in again.
I don't seem to have any air in the system - all the rads are nice and hot and no noises of air coming through when the heating is on. If I bleed the rads, it's just water.

I had it set at around 1 bar when cold. I watched the pressure guage and it drops by about .2 - .4 bar when it fires up and then returns once it's up to temps.

I filled the system with a bit more water and so it ran at 1.5bar when hot and around 1.3 when it's cold. The following day (after topping up), the noise had gone completely. The next morning it had come back slightly, so I put a bit more water in thinking maybe I didn't put quite enough in, so up to 1.8bar when hot. Again the following morning no noise. 24 hours later, the noise comes back...

It doesn't seem to be losing any pressure so I'm assuming it's not leaking, but now I'm out of ideas as to what it could be... any suggestions??

My pipes come out of the boiler and into my lounge, then up to the bedroom floor. I've got 3 rads upstairs and then 2 more that drop down for the downstairs.

I've cleaned the system with fernox F3, drained and refilled 4 times and put in F1 inhibitor.