Strange problem with Danfoss heating controls

[sonnyikea]

Hi All,
Long time reader, but not a regular poster.

I have a strange problem with my CH/HW setup. First I will list the parts.
Glowworm Boiler
Danfoss Electronic Timer with separate water and heating functions - 7 day programmable.
Cylinder Stat
Danfoss RX-1 room thermostat (all working fine red light on when stat is calling for heat, red light off when not, audible click between on and off)
Danfoss HSA3 3 port valve (recently replaced actuator head due to rads heating up when HW only was on)

When I say strange I mean in it's occurance.
I have the HW and CH set to come on at 6am. The HW is scheduled to go off at 6:40am the CH continues through until 8am.
At 6am both the HW and CH works. The rads get hot and the cylinder warms up.
At 6:40 the HW goes off and the CH (if the room stat is calling for heat) continues to work.
At some point around 7am the room stat is satisfied and the CH goes off.
It's at this stage something strange happens when the room stat calls for CH again.
The light on the timer is on to call for CH.
The light on the RX1 is on to call for CH.
The boiler does not fire.
If I turn the room stat down and back up again the RX1 light goes off and comes on again as it should and yet still no boiler firing.
If I leave the Controller CH call to on and turn on the HW on the controller the boiler fires (I've had a shower inbetween times and so the Cylinder stat is calling for hot water).
If I turn the HW off at the controller the boiler should still fire as the room stat and controller are asking for CH. This does not happen.
To get the CH to work again I have to turn off the call for CH at the controller. Turn on the HW at the controller again. Turn off the HW at the controller and then turn on the CH at the controller. This then allows the boiler to fire and the rads warm up.
Subsequent calls from the room stat stop and start the boiler as normal.

This has happened every morning for the past week.

However, in the evening I have the exact same timing arrangement but for CH for longer.
7pm both CH and HW come on.
HW goes off at 7:40pm.
The CH goes on until 11pm and works fine with the room stat doing the job of controlling the boiler firing depending on temperatures.

So, I am going to open up the wiring centre when I get a chance to see what is happening (first diagram here http://danfoss-randall.co.uk/PCMPDF/39917v05.pdf). I believe there is an issue with the 3 port valve but I'm not sure what. I don't think it is a mechanical issue as I would expect heating to be on when HW is called for or HW to be heated when CH is called for but I dont believe this to be the case.
Therefore is it something electrical? If so what?

As I will have to look at the wiring centre first thing in the morning I'd like to narrow down what I'm looking for in advance and get it straight in my head.

Any pointers gratefully received.

Thanks

Craig

 

[doitall]

I think you should rip the boiler out and fit a nice new combi.

What model programmer do you have, is there a clash with the RT1.

 

[sonnyikea]

Unfortunately thats not an option at the moment

I should have said that the system has been in for a number of years and has been working flawlessly (except for the recent actuator replacement) so there is no issue between the controller and the RX1.

It's the specific scenario that causes the issue, all other times the system seems to work fine.

 

[D_Hailsham]

Sounds like a wiring fault when the HSA3 was replaced.

Open the junction box that the HSA3 lead connects to.
Find the terminal which the grey valve wire connects to.
There should be two more wires connected to this terminal: one to the Cylinder thermostat; the other to the programmer.

Is one of the wires missing?

 

[45yearsagasman]

recently replaced actuator head due to rads heating up when HW only was on)

That usually is not the fault when the heating is coming on when hot water only is selected. It's usually a fault with the valve body being seized or not sealing correctly. Did you ensure the spindle moved freely before fitting the head?

 

[sonnyikea]

D_Hailsham - excellent. I remember these two wires when I fitted the replacement head. Perhaps one has come loose. Looking at the wiring diagram I linked to I thought it might be the grey wire that was the culprit.

I will check that tonight when I get home. Any idea why it works in the evening fine and the scenario is the same? Might it be that in the morning the HW is being turned off at the controller before the cylinder stat is satisfied or vice versa the cylinder stat is satisfied and then the HW goes off whereas in the evening the cylinder isn't satisfied prior to the HW going off at the controller (more likely as more water is used during the day)?

 

[sonnyikea]

recently replaced actuator head due to rads heating up when HW only was on)

That usually is not the fault when the heating is coming on when hot water only is selected. It's usually a fault with the valve body being seized or not sealing correctly. Did you ensure the spindle moved freely before fitting the head?

Thanks 45yearsagasman - yes I checked that the spindle moved freely, which it did. Since replacing the actuator head that particular problem went away.

 

[doitall]

Or it may be a fault with the programmer, but you choose to ignore that question.

 

[sonnyikea]

Or it may be a fault with the programmer, but you choose to ignore that question.

Not at all doitall I just didnt think there was a clash between thecontroller and the RX1 unit. There may well be an issue with the programmer. Is this something that goes wrong with the heating controllers? I did a hard reset of the controller but the problem remained. It also doesnt explain why it works ok in the evening, unless there is some software difference between the morning timer and the evening timer?

 

[doitall]

Let me think, it works sometimes but not others, so something is not working all the time.

Could be a broken wire if it wasn't so regular, same reason it can't be the actuator, unless you made a right hash of sticking the wires back in the box, and even then unlikely.

Having thought some more, the only thing that changes is time.

I asked for the model of the programmer, perhaps when I get back I'll have the details.

In the meantime, concentrate on the timer and the stat.

 

[sonnyikea]

The programmer is an FP715.

 

[doitall]

Out of interest why did you change the actuator, what was the fault.

 

[sonnyikea]

During the summer when the hw only was selected the rads were heating up. Spindle on the valve was moving freely. The actuator was making a constant clicking sound when HW was requested.

Since I replaced it that issue went away.

 

[doitall]

If you have a multimeter and know how to use it safely, I would check the outputs from the timer, and the communication etc from the stat.

If you can post a clear pic showing the wiring center we can check it out

 

[sonnyikea]

thanks doitall - I will check out all options tonight and let you know.

Appreciate the responses from all.