Strange problem with Danfoss heating controls

[D_Hailsham]

How a mid-position valve works

If the HW and CH are on and the HW goes off the CH never fires. The actuator doesn't move when the HW goes off. That's the root cause of the problem.

Either there is no voltage on valve grey wire (240Vac on terminal 7) or Switch S2 is not moving over (240Vac on terminal 6)

If the HW is on first and then goes off and then the CH comes on everything works fine.

This can only happen if the valve is moving right over. There should be 240V on Terminals 4, 6 and 7.

Likewise if the CH is on first and then goes off and then the HW comes on everything works fine.

So the valve is returning to HW position OK. The boiler is lit by the HW stat.

If the CH is on and the HW comes on both heat.

So the valve is moving back from CH only to mid-position. Check for 0Vac on terminal 7 and 240Vac on terminal 4.

If the HW then goes off, again the actuator doesn't move and the CH never comes back on again.

This where we came in!

The problem is something to do with the grey wire (terminal 7) not getting 240V when it should. There are two sources: programmer HW OFF; cylinder stat SAT terminal. Here's how you find out which it is:

Measuring AC volts is the same as DC, but make sure the meter is set correctly.
Touch black probe to a neutral in the vertical strip and red to appropriate terminal

Take proper safety precautions, i e, TURN POWER OFF at main connection before disconnecting/reconnecting any wires.

Disconnect the wires from terminals 7 & 16.
Set programmer to HW OFF.
Check for 240Vac on terminal 8
If no voltage possible break in wire from programmer or faulty programmer.
If T8 ok, check T7 - no volts means link 7-8 is faulty.

Disconnect wire from terminal 8 and replace wire in terminal 16
Set cylinder stat to low.
Check for 240Vac on terminal 16 If 0Vac, there is a break in wire from cylinder stat or cylinder stat is faulty.
If 16 is OK, check 240Vac on T8. If none check link from 8 to 16.

 

[doitall]

The problem is something to do with the grey wire (terminal 7) not getting 240V when it should. There are two sources: programmer HW OFF; cylinder stat SAT terminal. Here's how you find out which it is:

Sorry Dave that is not technically correct.

If the valve is not opening fully then the micro switch will not make and put 230V on the orange.

 

[D_Hailsham]

The problem is something to do with the grey wire (terminal 7) not getting 240V when it should. There are two sources: programmer HW OFF; cylinder stat SAT terminal. Here's how you find out which it is:

Sorry Dave that is not technically correct.

If the valve is not opening fully then the micro switch will not make and put 230V on the orange.

I agree, but in my defence I earlier said:

Either there is no voltage on valve grey wire (240Vac on terminal 7) or Switch S2 is not moving over (240Vac on terminal 6)

The easiest way to confirm if the switch has moved over is to measure the voltage on the orange wire. If it is about 100-150Vac the switch has not moved. Obviously it does work sometimes, but not when the valve just moves from mid-position to CH only.

 

[sonnyikea]

Thanks to all of you for your detailed advice and suggestions. I plan to go through everything with the multi-meter methodically this weekend. I will post back my findings.

 

[sonnyikea]

Posting this piecemeal:
At the actuator connector block I have the following

CH only from scratch
240Vac at Orange, grey & white

CH & HW
Grey 140Vac
Orange 240Vac
White 240Vac

HW Only
Grey 30Vac
Orange 240Vac
White 0Vac

Nothing on
Grey 240Vac
Others 0 Vac

When in the problem scenario HW & CH on and calling, HW no longer calls, CH still calling or off and then calling again
Grey 240Vac
White 240Vac
Orange 0Vac

CH stops calling, same values
CH calls again, same values

On to the wiring centre now.

 

[sonnyikea]

Take proper safety precautions, i e, TURN POWER OFF at main connection before disconnecting/reconnecting any wires.

Disconnect the wires from terminals 7 & 16.
Set programmer to HW OFF.
Check for 240Vac on terminal 8
If no voltage possible break in wire from programmer or faulty programmer.
If T8 ok, check T7 - no volts means link 7-8 is faulty.

240Vac on terminal 8
240Vac on terminal 7

Disconnect wire from terminal 8 and replace wire in terminal 16
Set cylinder stat to low.
Check for 240Vac on terminal 16 If 0Vac, there is a break in wire from cylinder stat or cylinder stat is faulty.
If 16 is OK, check 240Vac on T8. If none check link from 8 to 16.

0Vac on terminal 16
0Vac on terminal 8 (obviously)

So it's a banjaxed cylinder stat that I have?

 

[D_Hailsham]

At the actuator connector block I have the following

CH only from scratch
240Vac at Orange, grey & white

CH & HW
Grey 140Vac
Orange 240Vac
White 240Vac

HW Only
Grey 30Vac
Orange 240Vac
White 0Vac

Nothing on
Grey 240Vac
Others 0 Vac

They are all OK. The low voltages you sometimes get on the grey are due to the diode and resistances in the actuator.

When in the problem scenario HW & CH on and calling, HW no longer calls, CH still calling or off and then calling again
Grey 240Vac
White 240Vac
Orange 0Vac

There should be 240Vac on orange. This comes from the white wire via switch S2 (see the link I posted).

Why did HW stop calling? Water up to temp or turned off at programmer?

When the valve moves from HW only to CH only S2 moves over OK; but when it moves from mid-position (CH and HW) to CH only it doesn't move over completely.

Sticking valve?

0Vac on terminal 16
0Vac on terminal 8 (obviously)

So it's a banjaxed cylinder stat that I have?

Could be a broken wire from wiring centre to cylinder stat or a loose connection. Check voltages at the cylinder stat with HW on at programmer
C = 240Vac all the time
1 = 240V when stat turned up, 0Vac when turned down
2 = 0Vac when turned up, 240Vac when turned down
(the terminals may be numbered differently)
C goes to programmer HW ON
1 to Valve orange
2 to Valve grey

 

[sonnyikea]

There should be 240Vac on orange. This comes from the white wire via switch S2 (see the link I posted).

Why did HW stop calling? Water up to temp or turned off at programmer?

When the valve moves from HW only to CH only S2 moves over OK; but when it moves from mid-position (CH and HW) to CH only it doesn't move over completely.

Sticking valve?

The behaviour is the same regardless as to whether the programmer stops calling for HW or the cylinder stat stops calling (I believe). Having said that I have only tested exhaustively by using the stats. Due to the location of the timer versus the actuator, cylinder stat and room stat it is easier this way.

It exhibits the same behaviour with the actuator head off so it can't be a sticking valve right?

Could be a broken wire from wiring centre to cylinder stat or a loose connection. Check voltages at the cylinder stat with HW on at programmer
C = 240Vac all the time
1 = 240V when stat turned up, 0Vac when turned down
2 = 0Vac when turned up, 240Vac when turned down
(the terminals may be numbered differently)
C goes to programmer HW ON
1 to Valve orange
2 to Valve grey

I will check this out tomorrow evening.

Thanks for commenting on a Sunday.