Honeywell 3 Port Faulty ?

3 Apr 2008
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United Kingdom
Hi all, just wondering if anyone can help, on this one.

The problem I've got is the heating flow pipe from the 3 port valve (A) gets hot & rads get hot when HW only demand.
Heating works fine, it turns on/off at programmer and on/off at room stat
Hot Water works fine, it turns on/off at programmer and on/off at cylinder stat.

Boiler: Worcester 27Ri
Programmer: Honeywell ST9400C
3 Port: Honeywell 28mm (I assume a mid position)
Cylinder Stat: Honeywell L641A
Room Stat: Honeywell DE92E
My sparky has conveniently decided to go on holiday so I ended up wiring it myself. Hmmmm...

Here's how I wired it - hopefully it's right (n)

Terminal 1: Boiler Live, Programmer Live & Room Stat Receiver Live
Terminal 2: Boiler Neutral, Programmer Neutral & BDR91 Receiver Neutral
Terminal 3: Boiler Earth, Programmer Earth & Room Stat Receiver Earth
Terminal 4: CH On from Programmer (4) & (A) From BDR91 Receiver
Terminal 5: (B) From BDR91 Receiver & White from 3 port valve
Terminal 6: HW on from programmer (3) & COM from Cylinder Stat
Terminal 7: HW off from programmer (1), #2 from Cylinder Stat & Grey from 3 Port Valve
Terminal 8: Orange from 3 Port Valve, #1 from Cylinder Stat & LR from Boiler

Cylinder is the last tee in before the boiler.
3 Port Valve doesn't appear to be sticking as it's loose when I removed the head.
Would I be right I thinking its a case of the 3 port valve 'passing' and letting water through port A when it shouldn't ? Is this a common problem ?
Is there a way of checking or confirming this ?
I think I've got a spare 22mm 3 port valve in the shed, so I could try that in hand to see if the actuator moves the ball as it should. Are the actuators the same (22mm & 28mm) ?
Any help will be appreciated - thanks in advance
Last edited:
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