Megaflo and valve wiring for pump run on

[WhydidIstart]

Hi,
I would like to know how to wire a mid position and Megaflo safety isolation valve into a CH/HW system, but for a boiler that has a pump run on. Are there any modifications to the normal Y plan wiring (plus safety valve) as it looks like on HW only if the tank stat is satisfied the safety valve will close but leaving the pump on and water nowhere to flow.

Background:
I have an existing Megaflo tank that currently provides hot water via just the immersion heater. There is a mid position valve and safety isolation zone valve (comes with the Megaflo) connected to the indirect coil and central heating pipes – but not wired up to anything. There is no boiler (just a disconnected back boiler, never used and not connected to the system). Whilst decorating I am adding a programmable thermostat and replacing the controller for a proper programmable controller for HW and CH and in a better location.

A local plumber has been round to quote for installation of the boiler, but he wasn’t sure about the wiring for the valves. As I’m adding the thermostat, etc, I would like to have all this sorted so that he can get on with the boiler installation and check over the Megaflo piping and connect it all up. He said he can work on these cylinders but would prefer to just do the boiler installation.

It would seem that the 3 position valve would need to be able to switch to CH or HW+CH whenever HW was satisfied. Could it be turned round so that it flows to CH rather than HW as default, would that help? I under stand you would need a changeover room stat rather than HW switch to give a “CH not required” signal with the normal Y plan wiring… Are there any standard wiring diagrams for this??

Any help is much appreciated.

 

[Boilerman2]

As long as you have fitted an Automatic By-pass Valve, you do not need to worry about wiring as the Auto bypass will allow circulation whilst the over-run is functioning - why make it complicated?

 

[rojaca]

do not take pump live from blr switch live terminal in wiring block. pump will need to be fed from blr. Blr will prob require perm live, switch live, neutral, earth and pump live. Neutral and earth for pump can be connected in main wiring block. check blr manual for wiring diagram

ur right, bypass req'd as a positive shut off to dhw is a requirement on unvented

sorry if missing anything. too big a block of text.

Keep your posts short and pithy. much better chance of being read

P.S sounds like you might want to consider an alternative plumber-where areyou. somebody may be able to help.

 

[WhydidIstart]

Hi, thanks for the quick replies - bypass seems the obvious solution.

Sorry for the block of text. Reading through other posts looking for an answer people often asked for more info so I thought I'd put it!

 

[Agile]

To install an unvented cylinder requires an appropriate certificate. That particularly includes the wiring!

Your plumber sounds as if he MIGHT have the certificate but not the ability to do heating system wiring. Thats quite common.

The best thing to do is let him do what he can and then for him to bring in a suitably qualified heating engineer to connect/check the unvented cylinder.

I dont think its sensible for you to do the wiring yourself or pressurise him to do anything he is not comfortable with.

Nor should you or he call an electrician as they will normally not have the certificate.

Tony

 

[Agile]

Oops

 

[WhydidIstart]

Hi, he seemed familiar with the Megaflo tank and was expecting the second isolation valve, etc. I will ask if he has the cert to work on the tank, what should I ask about, is it G3?

I obviously want to end up with a safe and also working system so won’t ask him to do anything he doesn’t want to. I thought it made sense for me to do the wiring though partly as I’m fitting the programmable thermostat + controller and know where all the various wires in the area come from and go to.

Also partly if it gets too expensive then I will have to postpone the whole job for a few months which isn’t great as it’s cold now! Once done, it can then be checked for correct operation by the professionals which should be quicker than him doing the wiring and fault finding any problems with wiring elsewhere.

How come oops?