RWB9 programmer not turning boiler on

[barrowfordred]

My boiler is operated by a Siemens RWB9 programmer, this operates the heating and water, or rather it did until this week. Now, even though all the lights are on to indicate the system is turned on, the boiler doesn't fire. If I press the control unit the boiler starts up. I guess indicating a connection fault regarding the control unit. I've taken the unit off the backing plate, cleaned all connections (although they look fine) replaced the unit but it's still the same. The fault only seems apparent after the unit has been off for a while, It doesn't turn back on using the timer. I've reset the unit but still the fault persists. Any other ideas before I buy a new control unit.
I'll try taking the unit apart tonight to see if there's a connection fault in the unit. Strange this as the unit just sits on the wall and all I did recently was change the operating times. It's not worked since.
All thermostats are OK. Nothing has changed with these.The unit has an "advance" function which advances the operation onto the next setting. This morning the boiler didn't start, by the time I'd got up the timer has scrolled through to off anyway. Pressing "advance" turned the boiler on.

The boiler doesn't start at all on the timer. If I press on the timer unit it starts and operates as normal. Turning on and off via the thermostat.

It worked fine all day yesterday (after I'd got it going), but after it's been off for a while the control unit doesn't activate the boiler, although the 2 lights are on to indicate operation of the heating and hot water.

Any further ideas other than the timer unit is playing up?

My system is gravity fed heating with a 2 port valve on the heating but nothing on the hot water, so the heating can only be on with the hot water.
(Yes I know not the best system. I'm trying to find someone to plumb in another valve on the hot water side who doesn't charge an extortionate amount.)

 

[doitall]

If it was ok before you played with it yesterday, it's probably something you have done, be worth going back over the programs.

Before you waste an extortionate amount of money you need to find someone that knows how to convert the boiler/system to an S plan.

Could be expensive.

 

[barrowfordred]

Thanks for the reply, yes I'll have to give it a good coat of looking at and see if there's anything I've missed. But I'm guessing the programming is OK otherwise it wouldn't work when I give the unit a press. It's a though it isn't seated right on the backplate and making a bad connection, although I've taken it off and re-seated it numerous times.

 

[MANDATE]

Check the wiring to the back plate just in case there is a loose connection.
Also check the toggle switches are correct set.

 

[barrowfordred]

Thanks for the replies. I had another look last night, although I only had half an hour or so spare.
I checked the programming and it's fine. I changed the units battery and could get the boiler to start testing it in situ using the "advance" feature, but come this morning the unit failed to start the boiler again.
If I get chance again tonight I'll check the backplate connections.
I honestly can't see it being anything other than timer related. Because it's movement of the timer that gets the boiler started.

 

[barrowfordred]

Definitely a bad connection between the timer unit and the backplate. The heating came on this morning after I'd fiddled with it last night. Daren't touch it again

 

[Tipper]

Your 2-port valve could also be at fault because if the valve motor is faulty or the internal switches sticking then the boiler won't fire. Sometimes the valve is just plain sluggish and the boiler late to turn on.

Does the boiler fire if you move the valve open with the manual lever?

 

[barrowfordred]

Your 2-port valve could also be at fault because if the valve motor is faulty or the internal switches sticking then the boiler won't fire. Sometimes the valve is just plain sluggish and the boiler late to turn on.

Does the boiler fire if you move the valve open with the manual lever?

I checked the 2 port valve and it was already on despite the boiler not having fired.

 

[stem]

I checked the 2 port valve and it was already on despite the boiler not having fired.

Therein lies the trouble, when the programmer is 'on' it supplies a live to the thermostat, the thermostat opens the motorised valve, then when the valve is open it operates a microswitch that tuns the boiler on.

If the motorised valve is open and the boiler isn't running, then the microswitch isn't working. Often they fail intermittently, so work sometimes and not others.

 

[barrowfordred]

I checked the 2 port valve and it was already on despite the boiler not having fired.

Therein lies the trouble, when the programmer is 'on' it supplies a live to the thermostat, the thermostat opens the motorised valve, then when the valve is open it operates a microswitch that tuns the boiler on.

If the motorised valve is open and the boiler isn't running, then the microswitch isn't working. Often they fail intermittently, so work sometimes and not others.

Thanks for that, maybe there is a bad connection from the valve to the boiler behind the backplate which would explain why when I touch/press the timer unit the boiler lights. The cable from the boiler runs to the timer backplate.

 

[stem]

It's possible that the permanent live supply to the microswitch is picked up from the programmer.