Noisy lock shield valve (video)

System pressure is 1.0 bar when ambient, rising to about 1.4 bar when up to the flow setpoint of 72. The circulating pump is fitted after the boiler (1.5 meter in terms of length of pipework) in the flow primary and before the three two port valves for the three zones I have. The radiator in question is the first radiator on the downstairs leg of the heating zone so absolutely not the highest point in the system. The highest point in the system would be the flow pipe at the hot water cylinder which has an automatic air vent fitted (as does the flow pipe just above the boiler flow output.
 
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Change that lockshield for another one, elsewhere on the system to eliminate it from your enquiries.
 
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It may simply be a bit of detritus caught in the valve. As I said swap it out for another and give it a look/see/blow/flush while its out!

Flush the pipe to the rad as well, by putting a towel round it and injecting a bit of water into the system via the loop!
 
it's a British Gas 330 (glow worm) on an S plan. Sealed system.
The BG 330 is designed for a maximum differential of 20C while you have balanced the system for an 11C differential. This may seem to be OK as it's not greater than 11C, however it does create problems: the flow rate at 11C will be approximately double that for a 20C differential; the pressure loss through the heat exchanger at 11C will be about four times that at 20C; the pump will consequently be working much harder.

The pump will probably be set to max speed. Try setting to the middle speed (assuming three speeds) and rebalance to a higher differential (no greater than 20C). Remove all TRV heads and open fully any wheel-head valves before balancing.
 
I'll Give that another go. I have tried that before but although the differential across the boiler flow and return was approx 18-20 degrees for the first 15 minutes of heating being on, afterwards the return begins to climb as the TRV's close down, right up until the point that there is only about 8 degrees differential across.

Pump is on speed three as you suspected. The system is fairly large and so required the six meter setting according to the heating engineer we had out last year.
 
Do you have an Automatic Bypass Valve on your system? (It will be between the pump and the motorized valves and connect the flow to the return.)

The boiler differential will vary as TRVs open and close. The important thing is that it doesn't exceed 20C. The boiler will reduce output (modulate down) when TRVs close as less heat will be required to maintain the set flow temperature. This will affect the differential.

In your topic last Feb you said that the engineer could balance for 15C across the rads but only 10 across the boiler. The engineer also said he had take his measurement "upstream of the bypass".

Presumably he meant he measured the temperature of the main flow and return pipes. If the boiler differential was only 10C this means a higher return temperature which can only be caused by an open bypass. This is wrong: the bypass must be shut when a system is balanced. It doesn't need to be open as all rad valves are fully open (no TRV heads) so the system is running at maximum flow.
 
Yes we have an auto bypass valve. As for February last year - that guy turned out to be a bit dim shall we say since the automatic bypass was setup for a 2 meter head and hence fully open most of the time.

We got somebody else who set up the system properly. All radiators now get piping hot (which if you recall was the issue I had - rads not getting hot and i was told I potentially need a 25-80 pump)

This noise is literally the only issue now.

With the bypass setup properly the differential at the boiler achieves whatever you've set all the radiators to now. (Say 70-55 across all rad flow and returns - that's what you get at the boiler until things start closing down)
 
Good to know the balancing is now OK. (I have been reading last Feb's epic on the topic!!)

Which make/model TRV do you have on the rad? (Some TRVs have built-in balancing facilities, so this could be used instead of the LS valve.)

You could try opening the LS valve by 1/12th turn or less to seek if it has any effect.
 
If you have one radiator and one valve creating the noise and everything else is finey fine then I wouldn't think it's worth chasing it much further than a dodgy valve, especially if it quietens down once it warms up.
 
Good to know the balancing is now OK. (I have been reading last Feb's epic on the topic!!)

Which make/model TRV do you have on the rad? (Some TRVs have built-in balancing facilities, so this could be used instead of the LS valve.)

You could try opening the LS valve by 1/12th turn or less to seek if it has any effect.

Drayton RT313's on the downstairs.

I'll try that suggestion of 1/12.
 
Just a shame our RT313's don't have the balancing insert - but the Honeywell Valencias upstairs do. Oh well.
 

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