On 19/12/2017 21:14, Stefen diicks wrote:
I have recently replaced my old Honeywell ST699 for a ST799. My problem is
that the CH works when I only use the CH slider. the hot water doesn't work
when I use that slider. also the heating stops working when I use
both. any
advice would be most welcome.

Tell us a bit more about the system? i.e. What type of control valve(s)
does it have?

Have a look at the following "plans" and see if you can identify yours:

http://wiki.diyfaq.org.uk/index.php/...ols_and_Zoning


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/