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Heat with hot water together, or heat only!

Postby overheatedengineer » Mon Nov 05, 2007 11:15 pm

A similar problem to many on here. The CH is flat out whatever the system settings, unless the boiler is off.

Gloworm condensing boiler, Grundfos pump and Danfoss controls (FP715 programmer, room stat; HSV3 and HSA3 comprise the valve assembly)

When the HW is on so is the CH and CH will not respond to the room thermostat nor the manual on/off on the programmer. HW will respond to the programmer and the cylinder thermastat but also will stay cold when the CH is flat out.

The lever on the valve moves freely, though back driving the gears by the sound of it. I've removed the actuator from the valve and cycled the programmer to see if the actuator works and the drive rotates to three positions in response. The spindle on the valve rotates freely >360 deg in both directions when turned with the finger and thumb. The manual lever moves back to its set position if moved with the valve opened.

I'm at a bit of a loss for fault finding ideas. The only thing I can imagine is that the actuator can no longer drive the valve to the correct position although it has enough power to turn itself. Does anyone know the correct positions of the manual lever for each position of the valve? At present it only moves to just before the mid point. Should it move almost all the way to the MAN detent for some settings?
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Simply Build It

Postby htg engineer » Tue Nov 06, 2007 9:29 pm

Firstly check the actuator hasn't been left in manual position. and that the screws securing the actuator head are not too tight.

Remove the actuator head and tuen boiler on, turn the spindle so that only the pipe coming from A port heats up (central heating). Then try turning again so that heat is only going to B port. If this works then the valve is fine, sometimes the spindle can sheer off from the valve inners.

If the valve is ok, but still not working:

Replace the actuator head, fairly simple to change, just make sure you put the head back on the right way. A heating, B water.
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Postby marrtin » Tue Nov 06, 2007 9:49 pm

My first guess would be an electrical fault, possibly with a micro switch in the motorised valve.

Check this website for possible wiring diagrams.


All central heating wiring is at mains voltage and therefore potentially lethal. If you are unfamiliar with electrical circuits, please disregard this advice and obtain expert assistance.

The vale head is readily available as a separate item, and can be replaced without draining down.
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Postby overheatedengineer » Fri Nov 16, 2007 9:33 pm

Thanks for the ideas. I bought a new actuator last Friday and installed it. The HW and CH work just fine now and just in time for the change in the weather on Monday too. :D

First thing I did was to make a note of the existing connections and take a few photos with a digital camera before disconnecting the old one. A pretty easy job even after redressing some of the bare wire ends in the junction box before I checked the operation of the actuator after wiring it in before finally fitting it. A working actuator moves through 90 deg with an intermediate stop at 45 deg, for future reference.

One thing I discovered was that the installers had wired all the controls and boiler into the DOWNSTAIRS lighting circuit (the boiler etc is upstairs). A bit of a surprise considering when the house was rewired, circuits were put in in expectation of upgrading the heating system. :evil:
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Postby overheatedengineer » Mon Dec 03, 2007 11:08 pm

An update. The valve and actuator are still working fine. However the gland round the spindle on the valve is now weeping. Oh well, it'll just have to get changed when I get thermostatic valves fitted next year.
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Postby DONFRAMAC » Tue Dec 04, 2007 1:54 am

You should renew that valve body PRONTO, as it will blow the motor assy. you have just renewed,----- it happened to me. The actuator motor is a complex stepper-motor, with an electronic circuit inside the body, and a brass "quadrant" gear and drive-pinion. My circuit was totally fried, and the gears stripped.
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