Heating Programmer Question

[southside]

Hi All,

I have a question about the operation of the central heating programmer I have. It has a jumper on the back to switch between pump and gravity systems. I have a pump system installed in the house and obviously need to have the jumper set to this. If I set the jumper to pump, when I switch on hot water, the mid-positioner does not open to heat the water in the main cylinder. If I switch heating on, the heating operates as normal, if I switch both on - heating only works, the mid-positioner does not open to heat water.

If I set the jumper to gravity mode and turn on water heating, the mid-positioner switch opens and heats water, if I switch to heating only, it switches on both water and heat, the mid-positioner opens to both Heating and water (both work) - which I understand is correct as in a gravity system, water heating takes priority so will always open; and same when I switch for both heat and water heating - both work.

Does this mean the Programmer is faulty or is it a wiring issue for the heating system? We have just had an engineer in as for switching on the heating for the first time this year we have had a nightmare time after cowboys installed for the previous occupants - mid positiner replaced as faulty (heating supplied with hot water), pipes connected to water cylinder were soldered/welded in place, heating drain point was broken, circulation pump recently failed and we discovered it was soldered/welded on, mid-positioner heat switch cable was not wired into point where 240v would switch, header tank reported too low....

Question about the header tank as well.....our plumber reported it was too low. It is below the upper heat pipe inlet for the cylinder (if you think the flow for heating water in) but above the outlet pipe at the bottom of the two even those water is pumped around by the circulating pump. Is this too low and should this be above it?

 

[doitmyself]

I have a pump system installed in the house and obviously need to have the jumper set to this.

Do you mean that you did not have a pump and have had one installed?

If I set the jumper to pump, when I switch on hot water, the mid-positioner does not open to heat the water in the main cylinder.

So you have had the system re-piped so both CH and HW are pumped via the mid position valve?

Check that the valve is the correct way round. Port A goes to the rads; Port B to the HW cylinder; Port AB to the pump.

If I set the jumper to gravity mode and turn on water heating, the mid-positioner switch opens and heats water, if I switch to heating only, it switches on both water and heat, the mid-positioner opens to both Heating and water (both work) - which I understand is correct as in a gravity system, water heating takes priority so will always open; and same when I switch for both heat and water heating - both work.

I am confused😕. You talk about a mid position valve and now say you have a gravity system.

Do you mean that you have an open-vented system with a Feed and Expansion Tank in the loft (small tank). If so that is NOT necessarily a gravity system. A gravity system is one where the HW circulation is by natural convection, not pumped. Water priority depends on what type of valve you have. The mid-position valve does not give HW priority; the diverter valve does.

What make and model valve do you have?

 

[southside]

Thanks for response. We have always had a pumped system but let me explain, this is after we moved in:

1. Turned on to heat water and heating would come on. We had a faulty mid positioner changed.

2. Turned on heating after being changed - heating would not come on. Had this checked and found the mid-positioner cable for heating was not wired into correct point (wired to point that received no 240v).

3. Circulation Pump failed. This was replaced. Heating engineer re-wired the box that the Mid-Positioner, Circulating pump and Cylinder Stat were wired to as it was not wired properly.

During testing, found that when programmer switched to heat water, this worked. When programmer switched to heating, heat water came on. Heating Engineer said that only occurs when Programmer set to Gravity setting when we should have set to pump - this was confirmed and corrected. Heating Engineer left as all tests prior to gravity/pump setting successful. Whoever installed the heating system did not do a good job.

Later, when water heating came on, mid-positioner did not switch to heat water. When heating came on - heating worked. When all switched off, boiler did not switch off but continued to heat water.

I switched back to gravity setting and water heating worked and the heating system switchs off.

My question was, based on my issue, is this a wiring issue or the programmer faulty? Sorry if it's a bit confusing but this is my best way of explaining.

 

[doitmyself]

I suggested that you first check that the valve is the correct way round. Port A goes to the rads; Port B to the HW cylinder; Port AB to the pump.

Have you done this?

 

[southside]

Yes this has been done and is correctly installed.

 

[doitmyself]

Yes this has been done and is correctly installed.

That's good. Now we can check the valve is working correctly.

Are you comfortable working with electrics? Can you use a multimeter?

I'll assume the answer to both questions is yes.

The valve has five wires: blue, green/yellow, grey, white and orange. The tests involve disconnecting/ reconnecting the grey, white and orange wires. Follow the steps in sequence. Do not change anything unless asked.

Turn power OFF
Turn CH and HW OFF at programmer
Set HW thermostat to MIN
Disconnect Grey, White and Orange wires (make a note of their connections)
Turn power ON
Turn HW ON and turn HW stat to MAX
Boiler should light and HW side of valve get hot
Check boiler stops/starts when cylinder stat is turned down/up.
Turn cylinder stat to MIN
Turn Power OFF
Connect White wire to a permanent Live terminal
Turn Power ON
Turn cylinder stat up
Boiler should run and both CH and HW side of valve get hot
Check boiler stops/starts when cylinder stat is turned down/up.
Turn cylinder stat to MIN
Turn Power OFF
Connect Grey wire to a permanent Live
Turn power ON
Boiler should NOT run
Turn HW OFF at programmer
Boiler should NOT run
Turn Power OFF
Reconnect Orange wire to original terminal
Turn Power ON
Boiler should run and CH side only of valve get hot.
Turn HW ON at programmer
Boiler should continue to run and CH side only of valve get hot.

If those tests are OK the valve is working correctly.