Y system vented indirect - No hot water

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Radiators are totally working fine.. equal heat bloom on the Thermal imaging camera, but it shows the hot water is only getting halfway from the pump.to the cylinder, even when 3W valve is both positions

All 3 Radiators are all hot which proves flow from pump to 3W valve port A to rads and return.

So my initial thoughts are..

blocked 22mm flow pipe from valve port B to cylinder.

Or blocked cylinder.

Or blocked 22mm from cylinder to common return.

Or a combination of all 3!

Wierdly the HW cylinder is piped with flow from boiler at the bottom of the coil and the return at the top of the coil.

System is fitted with magnaclean filter and that has minimal magnatite, system is filled with x100 and has been regularly serviced.
 
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Has system been drained ,if so,possible air locked coil ?
Otherwise sounds like a blockage ,or the MPV is stuck in central heating position.
 
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Radiators are totally working fine.. equal heat bloom on the Thermal imaging camera, but it shows the hot water is only getting halfway from the pump.to the cylinder, even when 3W valve is both positions

All 3 Radiators are all hot which proves flow from pump to 3W valve port A to rads and return.

So my initial thoughts are..

blocked 22mm flow pipe from valve port B to cylinder.

Or blocked cylinder.

Or blocked 22mm from cylinder to common return.

Or a combination of all 3!

Wierdly the HW cylinder is piped with flow from boiler at the bottom of the coil and the return at the top of the coil.

System is fitted with magnaclean filter and that has minimal magnatite, system is filled with x100 and has been regularly serviced.
Can you use the manual lever on the valve to put it in mid-position? If the pipe to the cylinder then gets hots it looks like a valve problem.
 
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Has system been drained ,if so,possible air locked coil ?
Otherwise sounds like a blockage ,or the MPV is stuck in central heating position.

Is there an air bleed valve on the 22mm pipe for the cylinder?

Have you tried setting the pump for maximum speed?
 
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Shut down system, drained it all down..

Stripped down the 3w from the pump and all seems fine. Sits blocking port A untill I move the lever over then moves to mid position if put into manual. Port B has a visible gap.at all.times..

Time to check the port B feed to the cylinder and return.
 
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Here it is... 22mm feed from hot cylinder to the common flow return..

Blocked...

and we found the 46 year old HW cylinder is weeping.
 

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@terryplumb As the rads are working, (inso much that they are getting very hot) the only logical conclusion was the section from the HW cylinder back to the return common. Magnet test indicated a presence of ferrous material in those pipes.

So the cylinder is currently piped with the coil input flow at the bottom and return at the top. Is it worth swapping them to flow at the top and return at the bottom when the HW cylinder is replaced.?

I'm.planning to cut out / replace the affected returns pipework and power flush with x800 the remaining pipes before i put a new HW cylinder anywhere near it
 
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I would connect flow to top tapping as a general rule of thumb ,but in reality it won't make a lot of difference in terms of functionality
 
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I was looking at this issue when i replaced my HW tank.

I came to the conclusion that it's important if you have a zone valve with a vent on the HW feed. (As mine did).

The vent (Automatic or combined (!) ) is sometimes on the supply side of the cylinder, before the zone valve as its the highest point in the system but before the zone valve.

This allows air in the system to continue to vent when the zone valve is shut.

I removed my combined FEV from this point and replaced it with an AAV as this is still the highest point in the main system.

I thought going in at the coldest part of the tank (the bottom) would be technically better as it may speed up heating but left it top entry due to the venting.

I never found a technical reason for top in/bottom out on a pumped system. I suspect it's a throwback to gravity systems?

Interesting design point.
 
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