Central heating ignores wall thermostat when hot water on.

[timwhalley]

Hi,

I have a Siemens RWB9 Programmer and a Drayton digistat 1 thermostat. My problem is that if the central heating and hot water is turned on at the programmer with the digistat turned down so it should not turn on, the central heating comes on. When the hot water is hot, then the central heating obeys the digistat. I asked the central heating guy from the gas board who announced that it must have been wired up wrongly in the first place so is not covered under the maintanence. As it is quite some time since it was installed and the installers have now dissapeared I thought I would see if there is anything I could try myself.

The boiler is a condensing boiler, which heats the hot water in a cylinder tank in the bathroom. The RWB9 is set with switch 5 down (10 mode) which acording to the instructions will restrict me to not being able to have heating only. (Which I assume to mean central heating only).

So far I have checked the wiring at the RWB9 which is as follows:

N - Black
L - Red (two red wires)
1 - Yellow
2 - not connected
3 - Blue
4 - Red

I have located a honeywell box in the bathroom with wires going to a pump, thermostat on the cylinder and a 'mid position activator'. I looked at the wiring in there and decided not to do anything in there yet as we have a lot of connections!

When the hot water alone is on I notice that I am getting hot water being pumped through the pump in the bathroom, so my first question is have I got the switch position in the RWB9 set inccorectly to the 10 mode, should this be set to fully pumped, ie. 16 mode? Second question much more broad, anybody got any ideas what is wrong!

Many thanks

Tim

[humperdink]

hi there the programmer should be set to 16 to allow your heating to come on independantly of your hot water( ie if you advance your heating at the clock when the water is off), but if it has always been set that way it sounds like the problem may be your mid-position valve passing internally. - basically not closing off properly to the heating circuit and allowing water to pass through when it should only be going to your hot water cylinder
if you have service/breakdown cover this fault should be covered

ps if you have any work done recently on the heating system it might be worth checking the lever at the end of the mid-position valve to check it has not been stuck in the manually open position

cheers hope that makes sense

[timwhalley]

That may be the answer then, the dip switch is set to 10 not 16, so I will try it on 16. I thought that maybe 16 was the required setting if you did not have a cylinder, so left it on the setting that it was installed on.

Many thanks

Tim

[nicksheehan]

Hi Tim,
Did you manage to fix your problem?
I have the identical problem and would like to fix also if you can help

Best Regards
Nick



[quote="timwhalley"]That may be the answer then, the dip switch is set to 10 not 16, so I will try it on 16. I thought that maybe 16 was the required setting if you did not have a cylinder, so left it on the setting that it was installed on.

Many thanks

Tim[/quote]

[timwhalley]

Just to close this topic. I managed to locate the problem(s). First of all the dip switch should have been set to 16 as advised. However the main problem was that the logic was wrong. The system had been wired up wrongly, I dug through the documentation and found that THREE wires had been incorrectly done. I moved them to the correct positions and all now works fine. I think the job had been done as a fudge to get it working, so for the last few years it has worked but to the wrong logic. Probably costing me a fortune in extra gas!

Many thanks

Tim

[Aenka]

Hi Tim

Please could you help me with the wires. I'd like to move them to the correct positions.
As you can see it is similar to yours.

N - Black
L - Red (two red wires)
1 - Yellow
2 - not connected
3 - Red
4 - Blue

Many thanks
Anna