CH / Boiler Firing even though Programmer is set to off when room thermo is up!

[Mobileadam]

Hi,

I have recently had my programmer replaced to a Randal 715 with seperate controls for CH and HW. The programmer was set for a fully pumped system determined by the existence of a motorised valve and only two pipes connected to the boiler. However my problem occurs when the programmer is set to off for both HW and CH but the boiler still fires when the room thermostat is turned up!!!!

I have checked the wiring on the programmer and no connection is made to the 'HTG Off' as was the previous programmer (Randall 702), could this be the problem? I can get HW seperately recently and when just wanting CH this also works.

I have three wires going to the room thermostat but the yellow (wired to terminal No. 3) appears not be connected to the programmer's wiring plate.

I switch the programmer to 'gravity' based system and now the CH comes on only with the HW and is not effected by the room thermostat when the system is off.

Is there anything I can check to confirm what type of system I have?

and how is the room thermostat controlling the boiler directly?

Many thanks

Adam.

[Christian McArdle]

The good news is that you appear to have a fully pumped system capable of fully independent control. You bad news is that also appear to have selected a complete cretin to wire up your new programmer.

Any number of wiring faults could explain the behaviour you are seeing. Connecting one end of the thermostat to permanent live, rather than the programmer's call for heating is one of the likely ones. Don't worry about the lack of connection to "Htg Off". This is rarely used. The lack of connection to one of the thermostat's terminals may be an issue, however.

Christian.

[Mobileadam]

Hi Christian,

Sounds about right, I have since found out that when the room thermostat was installed it blew the fuse for the programmer. The original rmt was replaced and the system 'commissioned' by the installed.

I disconnected everything and reset the programmer etc and fixed a new rmt to the wall (a Honeywell direct replacement instead of some generic thing). Anyway everything appears to be working ok, I have checked the switched live to the rmt and it comes on only when the programmer is expecting it, so all looks good, although I will be monitoring the system for a while yet.

Adam.