Rads taking ages to warm. CH pump only runs when boiler is heating.

[richardindorset]

So we'll go for it being a fully pumped system then

In which case, according to the wiring diagram you supplied; in fully pumped mode the pump will run whenever either the CH or DHW are calling for heat. So whenever the boiler is 'on' the pump will also be 'on'. But It shouldn't physically cycle 'on' and 'off' with the gas burner itself. You can see from the diagram the only places that the pump should get a live from are the externally supplied 'permanent live' and 'switched live'. It's in no way linked to the gas burner.

Under normal 'running' circumstances, there should be a permanent live on the top L terminal, and a switched live present on the bottom L terminal, meaning the pump will receive power as per the diagram below, regardless of the position of the pump overrun thermostat.

View attachment 287657



When there is no demand from the external controls, the switched live is removed, but, the pump will run on, provided that two criteria are met:
1. The overrun thermostat is sensing a temperature in excess of 80.C and
2. The permanent live is present on the top L terminal to provide operating power

View attachment 287658

If either the permanent L isn't present, or the thermostat detects less than 80.C the pump will stop with the boiler. Once the temperature drops below 80.C the overrun thermostat changes position (to NC) and removes power from the pump.

You can see from the above diagram that the permanent live is required to keep the pump running when the switched live has gone. Which means that you won't get a pump overrun if the permanent live is missing.



After all of this, the presence or lack of a pump overrun won't make any difference to how quickly the radiators heat up, as the overrun only come into operation at the end of the heating cycle. And if the radiators do have their own motorised zone valve it would be closed and stopping water flow whenever the pump overrun was in operation anyway. Which begs another question. The pump overrun requires a flow route somewhere to allow water to flow from and back to the boiler do you have one? Edited as you do have a by-pass

Just had another more careful look at the junction box and there is another wire connecting the Switched Live to the orange wires on the valves! It's tucked away behind all the other wires and I missed it last night!

You can just see it going to the terminal with the green arrow. The brown wire is the Switched Live to the boiler which comes in on terminal 1, then goes to terminal 12 and from there to terminals 13 and 6. 6 is where all the valve demand wires come in.

Looks like its all sorted now! Thanks again!

 

[Madrab]

Usually the orange wire is the SL and comes from the 2 port valve. When the 2 port valve is energised - usually from a powered output from the programmer via a thermostat, there is a microswitch that closes and that connects the grey input live wire of the valve to the output orange wire. That orange wire then sends a 240V SL to wherever it's needed, usually the boiler SL. The pump would then be powered by, in your case, the overrun output connector from the boiler.

Good schematics here showing the typical wiring - http://octaveblue.co.uk/central_heating.html