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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> central heating wiring problem https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1370282482 Message started by starflip on Jun 3^rd, 2013, 7:01pm

Title: central heating wiring problem
Post by starflip on Jun 3^rd, 2013, 7:01pm

Hi all,

Does anybody happen to know how you can have hot water just to fire the boiler and not the pump (as there is only one valve on the hot water tank side. gravity system), but the central heating to fire the boiler and pump ?
Think is maybe something to do with the valve wiring ??

Title: Re: central heating wiring problem
Post by thescruff on Jun 3^rd, 2013, 8:44pm

As much info as possible please, include all makes and models. boiler, programmer, valve etc

If it's gravity primaries the pump shouldn't work when hot water only is selected.

Title: Re: central heating wiring problem
Post by Lectrician on Jun 4^th, 2013, 7:35am

Can you describe your layout in more detail, or post a photo of the boiler/valve/pump layout?

A valve in the HW gravity side sounds odd.

Title: Re: central heating wiring problem
Post by starflip on Jun 5^th, 2013, 6:43pm

Answered my own question in the end I think ? Its a pumped ch and gravity hot water system with 2 port valve on the hot water tank. Honeywell valve, but it looks as though someone has changed the valve over and the new one they put in is missing the white wire (only 5 wires, and the old one was 6 !) and this let the pump work for ch but not for hw it looks like on diagrams !?

Title: Re: central heating wiring problem
Post by Lectrician on Jun 5^th, 2013, 7:39pm

That still doesn't make much sense really. What's opening the valve? Us there a cylinder stat?

The extra white wire is simply a changeover contact, along with the orange and grey.

Photos would help.

Title: Re: central heating wiring problem
Post by thescruff on Jun 5^th, 2013, 9:56pm

That's why I asked for information, there shouldn't be a 2post valve on the gravity primary,where's the cold feed and vent.

You can change from the old 6 to 5 wires if you know what you're doing.

Title: Re: central heating wiring problem
Post by starflip on Jun 5^th, 2013, 10:04pm

Sorry cant get any photos untill next week, yes its controlled with a 2 channel programmer a tank stat, also a roomstat for ch. But as there is only a valve on the hot water pipe, as soon as that valve opens it fires the boiler and the pump meaning all the radiators get red hot and no control as its down to the tank stat. As its a gravity system it wants the valve to open and circulate naturally round the tank, with no pump.

This diagram seems right if the valve had this extra white wire ?!
http://www.google.co.uk/imgres?imgurl=http://www.timstephenson.me.uk/files/2012/01/cplan.png&imgrefurl=http://www.timstephenson.me.uk/houserefurb/domestic-central-heating-system-wiring-diagram-c-w-y-s-plan&h=641&w=702&sz=85&tbnid=kHkE6KqDmlWlRM:&tbnh=87&tbnw=95&zoom=1&usg=__-s4E3nKSjxiLOIr4xko8RzW8h1E=&docid=x7STaz0yus3SIM&sa=X&ei=EKSvUaf9J4Sd0wXbg4HABw&ved=0CC8Q9QEwAA&dur=2917

Title: Re: central heating wiring problem
Post by thescruff on Jun 5^th, 2013, 11:12pm

To answer the question I need to know the information as requested.

Where is the valve as well the flow or return.

To part answer, the pump is controlled by the room stat, the room stat gets it's power from t4 in the programmer, but that can depend on the make model.

Title: Re: central heating wiring problem
Post by Lectrician on Jun 6^th, 2013, 6:30am

You are trying to make your system fit a "C Plan" which is quite a rare setup (even though the site you link to says it is a common system).

If you truly do have a C Plan, then you should of had the 6 wire valve installed, and not the 5 wire. You could either swap the head with a new one (no plumbing involved, but expensive), or add a relay to take place of the changeover contacts. Perhaps not particularly straight forward for a DIYer.

HOWEVER, if you have the wrong valve fitted, and are missing the white wire, I cannot see how the pump would fire up unless the time control and stat called for it. So your rads would not get hot just because the HW was on....

There must therefore be another incorrectly wired part, possibly when the valve was swapped. Has the pump and boiler been wired into the same terminal?