Heating Controls.

[Parky]

I have "fixed" a problem, but I still don't know if there is something wrong with the system. What do you think?

Two zones of heating + hot water, individual motorised valves. All set to come on at around 6.30 am. Downstairs heating does not come on, but does come on when programmed at other times during the day. What I did was to re-programme the hot water and the upstairs heating to come on later, whereupon the downstairs heating does come on at 6.30 ! Could it be that if the hot water and upstairs heating come on first, the downstairs heating valve can't open against the pressure in the system with the pump already running? Or maybe the actuator is starting to fail and hasn't got enough oomph?
The downstairs valve is 28mm, the other two are 22mm. The system is 7 years old.
Comments please.

Parky.

[twotwo22]

I would set them all to come on at the same time without having to get up early like 10:30 then watch what happens to the actuator for the downstairs heating. It will have a lever that will move or can be felt to be loose if the actuator is working. The aim is to compare.
You can compare the levers of the 3 actuators to see what is happening.

You could unclip/unscrew the upstairs and downstairs actuators and swap them over and see if the problem moves to the upstairs heating. This would indicate an actuator fault. If the fault stays with the downstairs heating then it mat be water or valve body related.

Is the downstairs valve installed in the correct direction of flow ?

[stewamax]

http://www.lovekin.net/honeywell-motori ... aults.html has a readable description of fault-finding on Honeywell and Drayton motorised valves.
And re twotwo22's comment

Is the downstairs valve installed in the correct direction of flow ?

such valves usually have an arrow on the valve casing (not the motor) to indicate the direction of flow; they will work more or less successfully in the wrong direction but will often cause a quite loud thump in the system when opening or closing caused by the water flow being shut too suddenly.
And if one of the three valve motors hums noticeably when the valve is supposed to be open, it may not be the motor itself (dirt cheap and easy to replace on a 7-year-old system) but the valve itself sticking with corrosion or sludge (considerably more expensive and needs a drain-down to replace): it may be being forced fully open by the water flow when 'downstairs' is the first to be actuated/ but only opening partly otherwise.
Note that assuming the system has been wired correctly, at least one of the three valves should have opened (or the actuator within the motor thinks it is fully open...) before the pump starts pumping; if not you will get pump-over to the header tank (if the system is open vented) or possibly the pressure relief valve opening (for a closed system).