Y PLAN MID POS VALVE

[sparkyt]

Is it possible to wire a y plan system using a mid position valve if the timeclock has no hot water off terminal? Im sure it is possible but my brains gone dead as im trying to sketch it out. Any help appreciated thanks

 

[NozSpark]

What make & model valve are you trying to use?

 

[sparkyt]

HONEYWELL V4073A

 

[NozSpark]

Just had a look at my Honeywell sheet and it does seem to need a HW OFF to the grey wire

 

[steptoe]

has the clock got a HW on terminal?

Ive not seen a 2CH clock with no off terminals,

what clock is it?

 

[PC Electrics]

No. Not directly anyway, when using a Honeywell valve.

You could use a changeover relay next to the wiring centre to switch the 3PV between HWon and HWoff by energising the coil with the HWon signal.

 

[steptoe]

Without hw off it means that the only power supplied to the grey will be from the cylinder stat terminal 2, the power on the grey wire is what puts the valve into full heating only, so in effect to achieve heating only the cylinder thermostat needs to be energised all the time so that when the cylinder is up-to temp it switches power to terminal 2 (grey wire full heating only).This in effect looses control of the hot water(which costs pennies)

I remember when serving my time doing something similar to this using a standard run of the mill timeclock and a light switch to turn CH on or off, just means you have to have HW on all the time. single CH clock in effect.

 

[NozSpark]

Without hw off it means that the only power supplied to the grey will be from the cylinder stat terminal 2, the power on the grey wire is what puts the valve into full heating only, so in effect to achieve heating only the cylinder thermostat needs to be energised all the time so that when the cylinder is up-to temp it switches power to terminal 2 (grey wire full heating only).This in effect looses control of the hot water(which costs pennies)

This has just made me think... bad day explode head hurts now

If you wire the tank stat permanent live to common, NO to HW common on time clock, NC to grey

then the time clock com from tank stat NO & HW ON to boiler/pump live

Would that work???

 

[sparkyt]

current clock has no DHW off termianal and you cannot select heating alone only hw and ch together or hw alone. client reckons it works fine. am i right in saying i only need link from a hw off terminal to the grey cable on the mid valve to get heating only?

 

[NozSpark]

That would work, but it could also boil his immersion cyl when he has his heating on in the winter..

TBH it would be a lot safer if you changed the programmer and wired it correctly!

 

[sparkyt]

That would work, but it could also boil his immersion cyl when he has his heating on in the winter..TBH it would be a lot safer if you changed the programmer and wired it correctly!

thanks, problem is its been wired like that for years and customer insists it works fine and he doesnt want clock changing. they dont even use the clock either they just put hw and ch on constant and turn room stat up and down accordingly. i want to wire it corectly but am fighting a loosing battle at the min. originally went to wire new boiler with switch live as the previous one was only a 3 wire.

 

[NozSpark]

Unfortunately you can't win a losing battle... just cut your losses and run!

Just put a ote on cert/invoice stating you advised "xxxx" and that it was rejected (or something like that)!

 

[steptoe]

if customer is happy then why argue?

 

[Goldspark]

Sorry this is a bit late but it may help someone in the future:

That's the problem when you try to put things right and it goes pair shaped. I've found that it's quite common for Y plan systems to be running for years with no HW Off wiring connections. You'll turn up to replace a valve or programmer and then when you point out that it's not operating properly the customer will say "It was working ok before". It's usually where the system was wired by a DIYer or dare I say a plumber (bless them).

It's also typical to find 3 core flex with the g/y used as a live connection especially on Y Plan cylinder stats. This type of thing can be a bit confusing (and dangerous) when you're trying to fault find. Never take it for granted that a g/y is an earth and be careful if you're testing a live wiring centre whilst touching pipework or leaning against a hot water cylinder.

Here's an explaination and wiring diagram of a Y Plan BiFlow heating system: http://www.electriciansblog.co.uk/2012/02/y-plan-biflow-central-heating-system-electrical-control-connections-and-wiring-diagram/

Hope it helps.