Intermittent controller problem

[flanzm]

Hi guys looking for a bit of advice to diagnose a problem. I've got a fully pumped, 3 port valve central heating system controlled by a Danfloss CP715. I have thermostats on both the hot water tank and living room (basically it's a fairly standard install).

It's worked fine for years but just recently it's developed a problem where the heating and hot water will both come as scheduled (auto setting, both HW and CH red lights on). The hot water and rads both heat up but when the hot water tank reaches the set temperature the central heating will also go off even if the room temperature is well below the thermostat setting (both HW and CW red lights still on).

The bizarre thing is this only happens intermittently (say every couple of weeks) and I can always fix it by killing the mains to the control unit and then turning it on again. When I do that it the pump immediately fires up and the rads get warm again until the room thermostat turns it off.

I'm sure it's not the thermostat as that's just a switch and it works fine. I suspect it's a dodgy controller, but could it be the three way valve. I'm not familiar with how the internal logic of these controllers work, and I don't understand why a mains reset fixes it. Any ideas - I don't want to replace the controller if there is nothing wrong with it.

Thanks for any help,

Mike

 

[hertsboilers]

Hi Mike, if you change both programmer and three port, 100% you will cure the problem. Otherwise you need a multimeter to measure the out put of the programmer while the problem happens.

 

[flanzm]

Hi there - me again!

I changed the programmer to see if it made a difference and I thought the problem had gone away but it hasn't. So this time I am going to change the three port valve.

I am trying to change a Danfoss HSA3. I thought it should be a simple swap but I have removed the old one and I've noticed that the valve spindle slot which is key locked is 180 degrees offset from the old one (this is with both set to manual).

My question is why are they different - both heads are HSA3's ? The valve seems to be correctly installed A is Heating, B is HW. I just don't get why they are out by 180 degrees and I can't just slot this head on in the same position as the old. How do I fit this ? Can I just turn the valve spindle by hand 180 degrees ? Which way should I turn it ?

Sorry if this is a stupid question but just want to check as I don't want to break the new head or cause the wrong port to open by getting this wrong.

Thanks again for any help.

 

[ollski]

Yes you can turn the spindle. Dont these actuators have a picture of which way to heating and which to hot water?

 

[flanzm]

Thanks for replying.

Yes the actuator has pictures on it- physically it looks identical to the old one and shows A is Heating and B is HW so I've got no worries with the physical installation being correct. The only issue is why the spindle key is 180 degrees offset - it just seems strange to me.

What effect does the position of the spindle have on the ports? Are -180 degrees and +180 (if you see what I mean) the same in terms of valve open/close ? Does it matter which way I turn it ?

 

[Echo the husky]

If HW and CH turn on but then CH stops there is either a fault with the valve jamming or its electronics, or power is not getting to the grey wire of the valve when the cylinder is up to temperature. The cylinder stat and its connections would be the first place I would check. when the cylinder is up to temperature and the CH is on, there should be 240V on the valves grey and white wires, as well as the orange. If there is power to the grey and white but not orange, either the valve is not moving to CH only due to a mechanical fault or the switch in the valve that sends power to the orange wire is intermittently faulty. As turning the power off clears it it is likely a valve fault. When the power is cut the spring pulls the valve to hw only, perhaps freeing a mechanical problem with the valve, or correcting an intermittent microswitch problem.

The next time it happens, set the programmer to HW only, if after a moment it starts again, the fault is with the cylinder stat or it's wiring. It can't be anything else.

To fit the new head open the manual leaver place head over the valve body and release the leaver and at some point the parts will align and the head will go on.