Honeywell ST9400C timer and no hot water

[andsally]

Hi

We had new system installed about 18 months ago: Vaillant ecotec plus 624 system boiler, 2x 2 port Honeywell valves (one for hot water and 1 for heating) and an ST 9400C timer.

Have just noticed that when I programme the timer, if I set the hot water to come on at a time later than the heating time on, then the heating valve does not change position and stays in the "off" postion - no hot water. The indicator light on the timer remains on.

With the heating switched to "off" on the timer, or at a time on later than the hot water, then the valve opens as expected!

I suspect this could be a simple wiring fault but cannot believe that I have not noticed this before.

Any other suggestions please?

Thanks

 

[twgas]

Can you explain, more clearly, your on and off problem.
Are you saying you only get hot water if the heating is turned on?

 

[andsally]

For a long time we have had both hot water and heating set to constant, with heating also controlled by room stat, which we turned down at night time. No probs at all throughout autumn and winter.

We get hot water and heating together.
We get hot water only or heating only.

It seems as if we can only get both on together if the hot water is switched on first at the timer, either via a programmed time or via using the once/cont/auto/off switch on the timer...

 

[andsally]

It was the ST9400C programmer that was faulty. We replaced it and all is now working fine.

 

[MartinFP]

Identical programmer and symptoms. After reading this thread and this one //www.diynot.com/forums/plumbing/need-to-replace-faulty-honeywell-st9400c.372984/ I got in touch with Honeywell and after a few emails back and forth they have sent a replacement. The system now appears to be functioning normally. Thanks for the information, everyone.

M

 

[BSAchris]

It was the ST9400C programmer that was faulty. We replaced it and all is now working fine.

I've had the same problem,it's driven me mad,I can't afford to call out an engineer,but did check wiring to and from the 9400c and found that there was no power to the pump,although the l.e.d lights on the unit were on nothing was happening.....no hot water and no heating for three days,finally I tried the reset using the main power supply switch to the system,it took three attempts and I got hot water,but the system was not controllable ,I'm suspecting a faulty timer unit(bad relays).
So thanks for your posts I'm going to get a new timer/control unit.
Thanks all for all your posts

 

[Happyplumber]

There was a load of Honeywell programmers which were faulty ,thats the model affected

 

[Dce]

I found that if you tap the top right hand corner, where the relays are, it will work. Alternatively you can turn off the back light, that works too. I think there is not enough power for the relays, you might notice the display dimming when trying to activate the relays. Could try soldering on some new relays if you want the light on as well.