Ask the Question

JohnM20 · Joined: 06 May 2008 Posts: 5 Location: Derby

Hi All Plumbers and Heating Engineers

I have trouble with my central heating, the radiators have started to remain on and hot when the roomstat is turned down and even if the CH is OFF on the programmer. My first though was a faulty motorised valve and have replaced it. This didn't cure the problem even though the LED on the valve showed the CH side to be OFF (LED not lit). The prt was obviously open.

I have replaced the programmer, thinking that it must be that. First couple of days it was OK but the problem has started again. The roomstat and the cylinder stat seem to be swithching on and off OK when checked with a meter. What else can it be ? It's driving me mad.

All help most welcome. Thanks in anticipation.

John M

thescruff · Moderator Joined: 03 May 2003 Posts: 4164 Location: Bath

When the heating is off, is there power to the orange wire in the valve

JohnM20 · Joined: 06 May 2008 Posts: 5 Location: Derby

Hi thescruff

Just emptied the airing cupbard AGAIN and checked the valve. Yes, there is 240v to the orange wire ('call' terminal of cylinder stat) when heating is swithched off. There is no voltage to the white roomstat 'call' terminal. There is voltage to the grey 'sat' terminal of the cylinder stat if I turn up the temperature setting. It goes to zero if I turn it down.

Thanks for your interest so far.

Have left the airing cupboard empty !!!

John M

thescruff · Moderator Joined: 03 May 2003 Posts: 4164 Location: Bath

The orange should not have power when not calling.

Is it a two or three port valve, make and number would be good as well.

JohnM20 · Joined: 06 May 2008 Posts: 5 Location: Derby

Hi thescruff

The valve is a Horstmann 3 port Type F322m

John M

thescruff · Moderator Joined: 03 May 2003 Posts: 4164 Location: Bath

And it was a direct swop, same valve as before.

JohnM20 · Joined: 06 May 2008 Posts: 5 Location: Derby

Same make but different model, original was Horstmann Zoneplus Z322XL. Was told it was the same although this new one has an earth wire and has LED indicators to show which port(s) is/are live. Both valves have exhibited the same problem - but not continuously.

Could there be some connection with the cylinder stat ? Checking the wiring. Power from the HW terminal in the programmer is going to the terminal marked 'C' (call ? ) in the cylinder stat. According to the Horstmann leaflet, the valve orange cable should go to the 'Call' terminal of the cylinder stat but it goes to the other side of the cyl-stat switch which I have called terminal B.

Terminal A of the cyl-stat (SAT ?) goes to grey of the valve
Terminal B goes to the orange of the valve + blue of the pump + to boiler.
Terminal C (Call ? ) goes to the programmer

If calling for heat, there is continuity between B and C terminals
If not calling for heat there is continuity between A and C
There is never continuity between A and B.

Thanks for your continued interest.

John M

vince knight · Posted: Tue May 06, 2008 7:59 pm Post subject:

There should also be a core going from the grey(sat) terminal to the HW OFF terminal or the programmer.

Remove the core that comes from the cylinder stat call from the orange and see if you still have 240v on the orange?

Vince

vince knight · Posted: Tue May 06, 2008 8:01 pm Post subject: