Bang Noise Coming From Radiators

[micol]

Hi,
Looking for some help as going insane. Apologies for the size of post, but wanted to give as much info as possible.

Setup:-
Newly Installed in October;
Worcester 28i Junior Combi Boiler installed in upstairs bedroom;
Salus RT500-RF Wireless Thermostat;
6 x Kermi Radiators;
5 with Danfoss Bi-Directional RAS-C2 TRVs fitted;
1 with two lockshields to control wireless thermostat (Hallway);
Upstairs and kitchen 10 mm microbore used;
Hall and living room 8mm.

TRVs on all upstairs heaters on Flow side with arrow pointing in towards the heater to signify flow going in.
TRVs on downstairs were fitted to return side and have arrows pointing away from heater signifying flow coming out of heater. Have been told with Danfoss Bi-Directional TRVs, this is ok.
Hallway has two lockshields fitted, one with drain off valve.
All lockshield valves are fully open on all heaters.

Issue
Banging comes as random single thud and happens mostly on the hall and kitchen, but has been heard on the others too.
Due to random, cannot confirm, but believe it happens when boiler goes off, i.e. when thermostat reaches set temperature and sends the signal to the bolier.
Have checked all heaters by opening bleed and water comes out instantly which is telling me no air in any of them.
System was drained after a week and additive put in to stop corrosion. Issue happening before and after draining.

Can anyone advise what most likely cause would be ?

Thanks

 

[seco services]

get the installer back.

 

[micol]

Any Ideas at all as to the cause ?

 

[seco services]

have you checked the direction of the trv.
remove the trv's top and you'll see a grey part near the spindle and has an arrow to set direction of flow.

 

[micol]

yes, all TRVs checked.
On flow side, arrow pointing in toward the heater
On return side, arrow pointing away from the heater.

 

[seco services]

yes, all TRVs checked.
On flow side, arrow pointing in toward the heater
On return side, arrow pointing away from the heater.

the arrows either point up or down

 

[micol]

ok, sorry, should have said some TRVs are horizontal and some are vertical.

Horizontal ones on flow have arrow pointing in toward the heater.
Vertical ones on flow have arrow pointing up the way.

Horizontal on return have arrow pointing away from the heater.
Vertical on return has arrow pointing down.