Hot water issues (electrical)

[zooankski]

Hi all

I am having a very strange issue with my hot water.
Basically, and it appears intermittently, the boiler will not fire when there is a hot water demand from the timer and stat has not opened.
The boiler is a worcester Bosch Greenstar 30CDI system boiler.
My home heating and water are split into 2 sections and either section should fire the boiler.
Downstairs i have an Uponor UFH system which works very well and a heat demand fires it no problem. Upstairs i have 2 rads and a 2 port valve, a secondary pump which works fine, unvented hot water cylinder and 2 port valve with stat.
The live and switched live have simply been piggy backed at the boiler terminals and yet the boiler will not fire intermittently with a HW demand.
Checking voltages on the connection centre shows some weird and wonderful readings with standing 60-100v at the 2 port valves.
I can only assume either that i have a high resistance switch on the HW actuator or some issue with the 2 systems being linked at the boiler?
Suspect actuator switch is most likely i think as i have seen the boiler fire from a demand upstairs on occasion.
Can anyone confirm my thinking based on the diagram i have done?
I am also thinking that it would be best to isolate the up and down systems with relays to prevent any possible back feed??

 

[stem]

Your diagram looks reasonable. I got a bit confused where you using blue for live though...after considering blue as neutral for 23 years old habits die hard

Most likely either the motorised valve is not operating properly. It may be sticking, for example, although this is not so likely, because usually when they fail, they stay shut. Or, more likely its internal microswitch is operating intermittently as you suspect. This is what actually operates the boiler, as you show in your diagram.

Measuring voltages is difficult on systems with lots of interlinked components unless you disconnect the wiring as you may also be measuring several other linked components, which may include PCB's for example

When the fault occurs (ie the boiler isn't operating, and just the hot water is selected 'on')

1. Check to see if there is 230v across the boiler neutral and switched live. If there is, the boiler is faulty. If not..

2. Then check for 230v across the motorised valves Brown (L) and Neutral (N) that will show that the motorised valve is getting power from the thermostat OK or not.

3. Now check to see if the valve is actually open by moving the manual lever. It will feel loose and unattached to anything if the valve is open, you will feel a resistance if it's not. If the valve is open, now check for a live on the motorised valve's orange and grey wires. When it's open both should be live, if only one is live the switch is faulty.

I am also thinking that it would be best to isolate the up and down systems with relays to prevent any possible back feed??

There's no need, that is what the microswitches in the motorised valves are for.

 

[Agile]

A simple test would be to see if the HW valve opens when it is faulting.

If so then problem likely to be switch in the motor valve.

If not them measure the contact resistance in the cylinder stat.

 

[zooankski]

Thanks for the replies. The valve is opening so i will disconnect the signal wiring and check the switch to try and work out what is going on