Problem with CH (possible 3 port Valve)

18 Nov 2005
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United Kingdom
Just moved into a new house, and I'm having trouble with the CH system. I'm no expert on these, so please excuse any vagueness...

The boiler / CH / HW work fine when both set to timed on the controller, plenty of Hot water, and Radiators get hot.

If I go to switch the CH on by itself, outside the timer, nothing happens. Boiler stays on the pilot light, radiators remain cold.

I had a play about, and found that if i move the lever on the automatic 3 port valve (above the pump) to MANUAL, the CH then works, until the lever resets back to automatic (resets over night after CH switched off). The CH then stops working in stand-alone mode again, until i move the lever.

Ideas? Knackered valve? There is resistance in the valve when I move it to Manual (feels like a servo), and it does reset, so is it the valve or something else?
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After a bit more playing around, I don't think the 3 port valve is broken. I think the controller is wired up wrong? the symptoms are:

2 hours after he ch/hw timed cycle has finished, I put the CH on - boiler fires for a few minutes, then stops.
Played with room thermostat, but that is not starting boiler again.

Switch HW on, boiler fires straight away, stays on indefinitely.

I think the HW and CH might be switched around inside the controller - the boiler turning off after a few minutes when CH switched on might be because the storage tank thermostat has kicked in (already near full from last HW cycle?)
Anyone any ideas?
These 3 port valves do appear to give a few problems. It is not easy to understand exactly how they function.
First thing to understand is that when CH only is called for, the valve receives its power from the room stat. So that would be the first thing to check. If the wire going into the stat is live, that would prove the programmer/timer is correct for the CH. When the switch is made within the stat the white wire going into the 3 port valve should be live and you should be able to locate this at the terminal box and check it.

Likewise with HW only being called for, the wire going into the cylinder stat should be live and if it is, then this confirms the programmer/timer is correct for HW.

There is however another wire coming from the programmer/timer that needs to be 'live' under certain conditions.

The timer switch for the CH is a one way type, so it's closed or open
The timer switch for the HW is a two way type, so although one wire enters the switch two wires leave the switch. One of these is HW ON and goes to the cylinder stat and the other is HW OFF, the wire from HW OFF goes to the terminal block and connects to the grey wire of the 3 port valve. So again if the grey is live with HW OFF is another easy check.

In a somewhat similar manner the room stat is one way but the cylinder stat is two way. So when HW is satisfied the switch cuts off the supply to the boiler but now supplies the other wire leaving the cylinder stat and this wire joins up with the HW OFF wire which went to the grey wire of the valve. Again this can be checked.
If you can understand the various conditions and check it out it will prove if the timer is wired ok.
Having said that the 3 port valve is not easy to understand, but they do fail due to either the motor which has to turn a quadrant against a strongish spring, so it may not get to the CH only positon and even if it does there is a microswitch that has to supply power to the boiler which may have failed, but again this can be checked to see if orange wire from the valve is live. Also on the valve the spindle needs to be tested for stiffness as this won't help matters if it's stiff.
Hope it all makes sense
:rolleyes: :rolleyes: :rolleyes:
Results of testing....

Had a look inside the valve, microswitch operation seems ok. there are 4 wires from the valve, Grey, Orange, Blue & Brown/white.

I looked at what went live whenever i selected hw or ch, so here goes:

All Off - Grey Live

CH selected - Grey & Brown/white live

HW selected - Grey & Orange live.

Is this correct? selecting CH causes no noise from the valve, although selecting HW does, but still nothing from the boiler when CH selected.

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I've also just done the following -

CH set to on, and then ran all the hot taps to 'empty' the storage tank - someone told me this should kick the boiler in. It didn't, so all i have is no hot water!
All off grey live. Thats correct, the grey is live due to the HW OFF wire.

CH selected grey live due to HW OFF wire! and brown/white live due room stat calling for heat! that seems ok to me.

HW selected Grey and orange live! This is not how I understand it.

When calling for heat the orange will be live, this wire powers up the boiler/pump. but the grey wire will be dead.
But when HW is satisfied the cylinder stat reverses the connections, it cuts off the supply to the orange and makes the supply to the grey.

You may need to double check this in the 'calling for heat' and 'satisfied' conditions.

'Selecting CH causes no noise from the valve' Now this depends where the valve was before CH was selected. If you remove all power the valve will return to the initial HW position, otherwise you have a live grey by one of two methods. Either the HW is ON but has been satisfied so grey is live from cylinder stat. Or HW is OFF and grey is live. This being the case the valve will stay at the CH position so it wont move when you next turn it on.
When the valve does move from either HW positon or the mid position to the CH positon (CH only) the microswitch has to make the orange wire live, the alternative route through the HW side has but cut off.( either HW turned off or if still on it has been satisfied.
I had a situation where CH was ok when shared with HW but would not function alone. the problem was in fact a faulty microswitch, which I could not replace at the time so a replacement actuator head solved the problem. (since rectified the microswitch)
:rolleyes: :rolleyes: :rolleyes:
Hi, thanks for the help so far. I've made a diagram of the CH circuit, can anyone have a look and check it? it looks quite 'busy'. It's linked here. The bars with dots going across the terminal blocks denote interconnections between those points (saved making more mess outside the blocks!)

Nice circuit diagram. For clarity it's normal to leave the earth wires out and even the neutral wires. Then the live switching wiring is clearer.

Your diagram looks fine, except that it isn't clear which terminals you're connecting to on the cylinder stat. The COM (common) terminal should connect to programmer terminal 3 (HW on), the SAT (satisfied) terminal should connect to your junction strip terminal 6 and the CALL (for heat)terminal should connect to your junction strip terminal 4/8.
Just had a look at your wiring diagram which seems to fit all the requirements. That is assuming at the progammer 1 = HW OFF. 3 = HW ON, and 4 = CH on.
At the cylinder stat I note 'blue' and 'green' are used which is a bit confusing because 'green' is for earth and 'blue' is for neutral.
'Green' should be kept for earth and any other colours used for 'switched live' wires should be sleeved with red.
If this is how it is, then you can see you you can't have both grey and orange live at the same time when HW is selected.
It seems your problem may well be at the 3 port valve.
:rolleyes: :rolleyes: :rolleyes:
Yep, I'm thinking it's just the 3 port valve. I know, the wiring colours are off, I've just moved into this house, and some of the electrics look a bit 'shoddy' and they've obviously just wired up the Cylinder stat with a piece of 3 core mains flex!

Anyone recocmend the cheapest place for a replacement actuator head for a danfoss Randall HSA3?

Thanks eveyone for your help.

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