I've been having trouble with my boiler.  Due to my refusal to pay
someone an stupid amount of money to fix it, I have tried a bit of DIY.

Basically I have replaced two of the circuit boards and the boiler now
seems to work.

Unfortunatly the boiler only starts up when I manually open the Zone
Valves.  The times control box doesn't seem to have any effect on the
system at all (although it does have power, and seems to be turning
itself on and off at the correct times).

Does this sound like a problem with the control box, as the boiler and
pump start up when I manually open the valves.  Is the control box only
responisble for opening and closing the zone values automatically ?

Thanks for any advice

In article , 
TallJim wrote:

> Unfortunatly the boiler only starts up when I manually open the Zone
> Valves.  The times control box doesn't seem to have any effect on the
> system at all (although it does have power, and seems to be turning
> itself on and off at the correct times).
> 
> Does this sound like a problem with the control box, as the boiler and
> pump start up when I manually open the valves.  Is the control box only
> responisble for opening and closing the zone values automatically ?


If it's a standard S-Plan system with two motorised valves (one for 
heating, one for DHW) then each valve has four connections. Two (L&N: 
brown/blue) go to the motor and open the valve when power is applied. The 
other two (grey/orange) go to a microswitch which closes when the valve 
opens: one of these two wires should go to a permanent (except when 
isolated) live, the other goes back to the boiler call for heat terminal. 

If the system works correctly when you manually open either valve then 
the boiler side of the wiring all sounds OK. This would then suggest that 
power is not being delivered to the MVs when the programmer turns on and 
you need to follow through the circuit to see what is happening. MV 
motors do burn out, but the chances of both of yours failing together 
would seem pretty remote.

-- 
Tony Bryer SDA UK  'Software to build on'  http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.10 released 4 April 2005]

Thanks a lot Tony, that make lots of sence.  I think it is a S-Plan
boiler (Vailant 112E), and it does has 2 MV's.  I will try to follow
through the circuit to see it I can find the problem.  I assume if the
MV's are both still working, then the most likely problem is the
programmer ?  Although I can't believe so many things went wrong at
once.

In an earlier contribution to this discussion,
TallJim   wrote:


> Thanks a lot Tony, that make lots of sence.  I think it is a S-Plan
> boiler (Vailant 112E), and it does has 2 MV's.  I will try to follow
> through the circuit to see it I can find the problem.  I assume if the
> MV's are both still working, then the most likely problem is the
> programmer ?  Although I can't believe so many things went wrong at
> once.


If it's an S-Plan system, have a look at the S-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm

You will see that the CH MV is fed from the programmer via the room stat.
Similarly, the HW MV is fed from the programmer via the cylinder stat. Both
valves have a pair of 'volt-free' contacts (i.e. electrically isolated from
the motor feed). When a valve opens fully, these contacts close. One side of
each pair of volt-free contacts is connected to permanent live. The other
side is connected to the boiler and pump (or just the boiler, if the boiler
controls the pump to provide pump over-run). So, when either or both
circuits are demanding heat, the appropriate valve(s) should open and - in
turn - switch on the boiler and pump.

So you need to trace the wiring for each circuit - from the programmer,
through the stat to the motor - to see what is live when it should be, and
what is not.
-- 
Cheers,
Set Square
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Please reply to newsgroup. Reply address is invalid.

On Tue, 13 Sep 2005 06:14:12 -0700, TallJim wrote:


> Thanks a lot Tony, that make lots of sence.  I think it is a S-Plan
> boiler (Vailant 112E), and it does has 2 MV's.  I will try to follow
> through the circuit to see it I can find the problem.  I assume if the
> MV's are both still working, then the most likely problem is the
> programmer ?  Although I can't believe so many things went wrong at
> once.


In between the timer outputs and the zone valves there  may be thermostats
on the wall and HW cylinder. as needed. 
-- 
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk 
Gas fitting FAQ  http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html