central heating thermo rad valves

[toptinker]

hello. just fitted new thermostatic valves to 5 radiators in my house
i cleaned and flushed all the rads and when i refilled the system added some inhibitor and some boiler noise reducer. after switching the heating on (all rads set at no 5 hottest) it seamed to run fine after bleeding all the rads. but when i turn down all the rads to approx no 2 the boiler kettles and bangs alot (as before) i have read etc that u should always have 1 rad valve set on the highest is this correct, did try this for 10 mins and the boiler did seam to run better ? (open vented system) any ideas ?

 

[kevplumb]

sounds like you need a bypass

 

[seco services]

how many rads have you in total? 5

 

[doitall]

Agree with KP it needs a by-pass valve, but even so one has to wonder why the boiler stat doesn't shut down.

What is the make/model of the boiler

 

[bengasman]

Or just stick to lockshield valves in the room with the roomstat; saves you having to pipe in a bypass. Unless you have a conventional boiler with zonevalves.

 

[toptinker]

cheers. there are 5 radiators. it is a myson economy boiler (approx 20 years old) there is a bypass valve fitted near the pump. not sure if ths should be fully open or closed . how do you set it, i think it is slightly open at the moment. the kettle/ knocking etc is not that bad it only seams to do it with the heating on, never when i use the hot water. there is are no room stats just the boiler stat and it does kick in and outwhen the system is on ?

 

[twgas]

try opening the by-pass valve a little (with the system on) and see if the noise abates. Be warned the valve itself might leak when you adjust it.

 

[bengasman]

Bypass should be automatic; creating a "leak" by sticking a gatevalve between the flow and return is a poor solution.

 

[twgas]

Bypass should be automatic; .

OP says its 20 years old - dont remember having to be auto by-pass in them days.

creating a "leak" by sticking a gatevalve between the flow and return is a poor solution.

I didn't mean "create" a leak, I meant a gate valve might leak when it's used, if its old.

 

[bengasman]

You are probably right about not being compulsory to have an automatic bypass 20 years ago. It should be automatic from a performance and efficiency point of view is what I meant.
The "leak" I referred to, is the produced heat "leaking" back into the boiler via the bypass, causing a higher cycle frequency and a slower response for ch and dhw.
I have a habit of forgetting that the rest of the world is not as mad as I am, and therefore won't always understand how my twisted my mind works.
Apologies for that. Don't worry, I may be mad, but am friendly and mostly harmless.

 

[toptinker]

cheers for your input. the bypass valve seams just to be a gatevalve. not really done anything with it. when i did open it there was a rapid gush of water, so that tells me it should be open just a touch. this valve i replaced approx 8 years ago as just a gate valve, should it be a thermo type valve ? also all the lockshield valves on each rad i fully open till the heating got hot then i closed them say turn and a half. just as a guess got no gauge, any better way ?

 

[twgas]

ABVs work on pump pressure rather than temperature.

 

[toptinker]

dont understand. is the byepass valve ok as it is or should i open it a touch?

 

[kevplumb]

try it

cant do any harm

 

[D_Hailsham]

dont understand. is the byepass valve ok as it is or should i open it a touch?

You said you have a Myson Economy; do you mean Economist? If so the installation instructions say:

To adjust the by-pass

The boiler should be fired with a full load, i.e. central heating and hot water and by-pass fully closed. The system should be balanced and fully vented. Adjust the pump to give a temperature rise across the boiler of 11°C (20°F). The boiler should then be switched to domestic hot water only. If noise is experienced under these conditions, the by-pass valve should be gradually opened to increase the flow rate through the boiler until the noise stops.

As for balancing , you said: also all the lockshield valves on each rad i fully open till the heating got hot then i closed them say turn and a half. just as a guess got no gauge, any better way ?
A valve which is a trun and a half closed is, to all extents, still fully open. You need to work between closed and one and a half turns open to balance the system properly. It is very sensitive, so work with eighth turn changes at a time.