Combi boiler heating wiring?...

[peterhawkins]

Is a combi boiler hard to wire up or easier than a conevntional system such as a s plan or y plan?? I ask as i have moved into a new house, with a combination boiler, and the hot water is great, very hot. THe heating though when tested didn't seem to come on. There is an old programmer / timer in the kitchen that says HTG and HW (obviously there is no use for the HW side as it is instantaneous).

Is it difficult to wire up the programmer and a room stat to the boiler so I can have heating and control of it? I have wired in components on my old Y Plan before and understand how the controls link together, but never wired up or learned how a combi boiler is wired up before.

If anyone can spare some time to help me I'd gladly buy them a pint or 2!!

 

[mogget]

Usually combi boilers are fairly simple for just the hot water and one heating circuit.

What make/model of boiler is it, and do you have the manual?

 

[peterhawkins]

Hi mogget, thanks for replying

There is a switched unit with a light indicator next to the boiler.

This has to be on for the h/w to work. So I am guessing combi boilers need a permanent supply to them, unlike my old boiler in my old house which had a swicthed live, along with the grundfos pump.

The boiler is a worcester (sorry do not know what make / manual is in the house in nottingham, am going back and forth moving in, so will be back there on tuesday)!

It is not a condensing boiler, but has a prv through the wall, and i saw a red expansion vessel at the back, and there is a filling key attached to the bottom panel of the casing.

I will of course report back I go to my house again, with the make/model of the boiler, and have a look at the manual.

If you could briefly explain how combi's are generally wired up, so I have an idea in my head, then I would be most grateful.

I am thinking they are like this: swithced live for heating, permananent live for h/w, neutral and earth??

And the switched live to the programmer/timer - to the CH on terminal. Then from the CH on terminal a wire to the COMMON terminal of a room stat (as per normal systems)?? obviously without the need for a wiring centre???

am i close or way off??

 

[bengasman]

Throw the old timer away, and either stick a WB clock in, or a programmable wireless roomstat; siemens rev24rf set is dog's whatsits, honeywell 927 not bad either.

 

[peterhawkins]

Thanks for helping.

Sorry but what is a WB clock?!

If i choose a programmable wireless room stat where do i stick the receiver? just under the boiler? and what wires go to the receiver generally?

 

[bengasman]

Sorry but what is a WB clock?

Worcester Bosch

If i choose a programmable wireless room stat where do i stick the receiver? just under the boiler?

Higher is better, and free of metal obstacles in the direction of the transmitter.

and what wires go to the receiver generally?

230volt plus 2 switch wires. Simpler than simple for WB boilers.

 

[peterhawkins]

Oh yes i remember now, some worcester boilers have a digi stat (wireless) and the boiler has a built in receiver. I'll see if mine has a built in receiver on tuesday!

WHen you say 2 switch wires, you mean call and sat ?? so to a programmer you would need to use CH on and CH off terminals??

 

[mogget]

With a combi you have a permanent live (and neutral, and earth) to the boiler - it wouldn't be able to fire up for hot water otherwise.

If yours is anything like my old Worcester you will have three terminals - Ls, Ns, and Lr. Connect the Ls and Lr terminals and the boiler will fire up for heating! Simples

If you already have, or can easily run, a wire from your boiler to your room stat, I would recommend a wired stat rather than a wireless one.

A programmable stat combines time and temperature into one box and usually is battery operated. These have just two (volt-free) switch terminals so you can use just one piece of twin and earth between the stat and the boiler.

Wireless stats work in a similar way but instead of the switch contacts being in the stat itself, they are in the receiver. The receiver also needs to have a permanent mains supply so it can 'listen' for the radio requests from the stat.

 

[peterhawkins]

Sorry, theis LS, LR is this the switch from the boiler to the stat??!!

On a conventioanl boiler you have 1 wire from the boiler, with a neutal, earth and live (switched live) which is powered, along with the pump, when either the room/cyl stat call for heat, via a MV in the case of htg.

With a combi, when the room stat calls for heat, the LS becomes live? I am confused about this LR, NR??!! ....

 

[mogget]

The stat itself is the switch

The three terminals are for external controls:

Ls = Live 'supply', to external controls
Ns = Neutral 'supply' if your controls need a neutral
Lr = Live 'return', switched live from controls

So if you wire a switch across the Ls and Lr terminals you will have control over the heating side of the boiler. It doesn't matter whether that switch is an ordinary switch, a room stat, or a programmable room stat, it makes no difference as the boiler sees it.

You need a programmable room stat for time and temperature control, but the boiler just sees a switch.

 

[peterhawkins]

Thanks for explaining I get it now!! Basically it is like a normal standard room stat, the COMMON terminal being the switched live, and the CALL terminal being the switched return!! and obv the N/R being the neutral if the stat requires a neutral (ie as an anticipator)!!...

So I will have 3 cores from the boiler, going to the prog room stat (or maybe just use a 2 core) and job done....

 

[mogget]

That's right.

If you get a battery powered stat such as drayton digistat 2/3, siemens rev11 etc, you wire it like this

Untitled

• mogget
• 31 May 2009
• 1

Not too difficult once you know how

 

[peterhawkins]

Thanks for your help, I feel a lot more confident now and will understand what I'm doing!!

Is the digistat like a normal stat but (obviously) with a digital display being the difference, and it is programmable?? I know you can get digi room stats that are not programmable and just have a digi display instead of a dial .... and of course, some do not require a neutral, so the battery in the digi stat provides the same function as the neutral wire would (for the anticipator)

 

[mogget]

There's no anticipator as such on a digital stat, as its function is provided by the software. Usually they are battery powered and don't need a neutral. The batteries last a long time, a couple of years usually.

A programmable stat means you can set different temperature setpoints throughout the day. Here's an example of a program.

At 0630, heat house to 21 degrees.
At 0900, heat house to 18 degrees.
At 1730, heat house to 21 degrees.
At 2230, heat house to 12 degrees.

So the heating would come on at night only if the weather was cold enough that the house temperature fell to 12 degrees.

You can also get ones where you can set different programs for weekends or weekdays, etc.

 

[peterhawkins]

Thanks mogget, agile and bengasman. I owe you all a pint or 3!!

One last q - if i buy a programmable did room stat, i only need 2 wires from the boiler, ie a SL and SR to the stat. And no neutral (depending on the stat tho).

I will check the boiler manual when i see it on tues anyway to be double sure.