Radiator questions/Central Heating

4 Jun 2008
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United Kingdom
Hi - I am studying central heating as a module. I have a few points that I think is right but would be appreciative if anyone could tell me if the following points are wrong/or could be slightly added to.... Thank you for your time help and advice. Best wishes, James.

first point: if one radiator is not warming up at all the reasons could be:
TRV pin is stuck
TRV sensor head is faulty
Sludge in the bottom of the radiator

are there any other common reasons?

second point: the point of an injector tee is: used for gravity primaries (as with solid fuel boilers) - to allow the gravity return to flow through the boiler and circuit at a better flow rate?

point 3: A bypass circuit and automatic bypass valve is ideally fitted when a system with 2x2 port valves and/or TRVs is used. As the TRvs close and the pressure goes above the pre-set limit on the auto bypass valve, it opens and allows the weater to flow around the bypass circuit, thus preventing a slow water flow rate through the boiler, and possible kettling and damage to the boiler heat exchanger. Although a lot of modern boilers (system boilers) have bypass circuits built in now. BUT a heating system using a 3-port mid position valve does not need a bypass valve at all - as there is always at LEAST one port open??

point 4: When removing a rad fitted with a TRV a TRV cap should be used and the sensor head removed to fully shut off the water flow to the radiator. And not all TRV caps fit all TRV's!!

thanks again for any extra help you can give me and any corrections to my above findings...
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System not balanced could also be a cause on rad not heating as could air lock.

Y-Plan still requires an auto by-pass (Part L) but you could also have an unlikely situation where HW satified, TRV's shut down, customer takes off the only non-TRV'd rad off (decorating) with r/stat calling.
hmm ok thanks for that advice. I know Part L1 states bypass valves/circuit to be installed but It doesn't make sense as a 3 port mid will always have 1 port open anyway!!!! strange..
second point: the point of an injector tee is: used for gravity primaries (as with solid fuel boilers) - to allow the gravity return to flow through the boiler and circuit at a better flow rate

This is only an issue when pumped CH is activated. The injector tee helps prevent the pumped side from starving the gravity primary of circulation thus increasing HW recovery time.
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thanks for your help guys so far. one other point i forgot to check / ask?

when a 3 port mid position valve is only calling for heat the orange wire is made live (as it is connected to the same terminal and the calling (usually number 1) of the cyl stat.(and also pump and boiler)

when heating and hot water are calling - white becomes live as well as orange

when only heating, white grey and orange from the 3 port mid position valve are all live??

lastly when hot water and heating are both satisfied the orange wire will remain live (unless the programmer is turned off or power is removed from the spur? and the valve will be held in its last position. But when power is off/programmer is off, the valve closes off port A?

am i correct here or have i got something wrong?
sorry to be a nusiance again - but was i correct or incorrect about the wiring of the motorised valve as in the previous post? thanks for your time.
if i am right-with a 3 port mid valve (honeywell anyway) - but most are standard colored wiring - hot only and the orange is live (as it is connected to call from the cylinder stat), white and orange: hot water andheating on (valve in mid position), grey white and orange (heating only on) and if hot water and heating are both satisfied-orange remains live until the programmer is switched to off.

a while ago i used a volmeter to test to see if my cylinder stat or 3 port was faulty. and as call n the cyl stat made to connection when it should have done i knewthat it was that which was faulty! this is how i remember the wiring as above!

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