Perm and switched live to new boiler?

[Agile]

You CAN use the existing switched live as the new switched live and take the permanent live from a nearby mains supply. Its not ideal but as long as the boiler is clearly labeled accordingly it CAn be done.

Alternatively, at additional cost, a wireless operated switch can be used to provide the switched live with the original supply to the boiler connected to provide the permanent live.

Tony

 

[D_Hailsham]

You CAN use the existing switched live as the new switched live and take the permanent live from a nearby mains supply. Its not ideal but as long as the boiler is clearly labelled accordingly it CAN be done.

Agreed, but it's still dodgy. It's always safer to assume that the next person who works on a system is an idiot.

Alternatively, at additional cost, a wireless operated switch can be used to provide the switched live with the original supply to the boiler connected to provide the permanent live.

I was trying to work out a wireless solution, but couldn't come up with one. What sort of wireless switch were you thinking of?

 

[Agile]

There are one or two designed for the purpose and within the last few weeks someone kindly quoted the model for me.

Even without using the dedicated item, any wireless stat with the temp turned up too high could be used with the required switched contacts wired between the battery or sensor connections.

Tony

 

[stem]

You CAN use the existing switched live as the new switched live and take the permanent live from a nearby mains supply. Its not ideal but as long as the boiler is clearly labeled accordingly it CAn be done.

Not according to section 11 of the Flexicom manual posted by the OP. On page 37 of the manual under "WARNING" it states

● Connection of the whole electrical system and any heating
system controls to the electrical supply must be through a
common isolator.

 

[pmx_super]

What components do you have in your airing cupboard?

Currently (and I'll try to be exhaustive, since I'm not sure if you mean heating system components or electrical components):

- Analogue time controls
- HW Cylinder, thermostat and electric immersion heater
- Grundfoss pump
- two silver boxes mounted on pipes (!?)

 

[stem]

- two silver boxes mounted on pipes (!?)

Two port motorised valves maybe

Untitled

• stem
• 26 Mar 2010
• 6

- Grundfoss pump

That would also need connecting to your new boiler if you went for the Flexicom.

 

[D_Hailsham]

- Analogue time controls
- HW Cylinder, thermostat and electric immersion heater
- Grundfos pump
- two silver boxes mounted on pipes

That's what I was looking for. The silver boxes are probably motorized valves as "stem" suggests. Unfortunately it only confirms that you have a problem.

Any boiler which requires pump overrun will mean that you have to run a cable from the boiler to the airing cupboard for the pump. This is in addition to the switched live and any supply for the valves, timer etc.

Would it be possible to pull through a new cable using the old one as a draw wire? You would need a four core plus earth. (live, neutral, pump live, switched live, earth).

 

[stem]

I would go for the Baxi that "sambotc" and "londonboy" have said doesn't need a permanent live. If that is the case, obviously no pump overun either (because there's no live to operate it when the boiler goes off) so all wiring can remain as is.

 

[Gasman77]

Viessmann 100 compact can be used without pump overun if it helps? havent read the whole thread......

 

[kevindgas]

In which case how about a pipe stat in airing cuboard ??? seen this done a few time's , wether the boiler manu' would were it , u could ask ????

eh? NO! you would only create a 2nd switched live route and the boiler would not shut down until it overheated!

 

[stem]

I think the suggestion was to connect the boiler to the switched live and the pump to a pipe stat wired to a permanent live in the airing cupboard, so that the pump would keep running until the water in the pipe had cooled sufficiently.

This raised a couple of questions in my mind, such as when the boiler first fires up and the pipe is cool, what would start the pump going? The pipe wouldn't heat up and bring in the stat without the pump circulating the water. If the live that switches the boiler was used to start the pump, then at the end of the heating period the 'live' from the pipe stat would also feed back to the boiler and keep it going.

You could get around the pump overrun with a relay that can be set to de-energise several minutes after the boiler went off.

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• stem
• 12 Jan 2010
• 3

But then does the permanent 'live' supply any other part of the boiler circuitry that may not function if it was missing such as a frost stat for example.

 

[stardanny]

Why don't the heating installer run new cable from boiler to airing cupboard.....?

I don't see why it can't be done.

Just lift carpet, lift floorboard, run cable where existing cable is, refix floorboard, refix carpet. Easy job.

If the programmer / timer is in airing cupboard, you only need 4 core and earth.

 

[transam]

In which case how about a pipe stat in airing cuboard ??? seen this done a few time's , wether the boiler manu' would were it , u could ask ????

eh? NO! you would only create a 2nd switched live route and the boiler would not shut down until it overheated!

Don't see that , as ther e would only be a switched live to boiler ????

 

[transam]

I think the suggestion was to connect the boiler to the switched live and the pump to a pipe stat wired to a permanent live in the airing cupboard, so that the pump would keep running until the water in the pipe had cooled sufficiently.

This raised a couple of questions in my mind, such as when the boiler first fires up and the pipe is cool, what would start the pump going? The pipe wouldn't heat up and bring in the stat without the pump circulating the water. If the live that switches the boiler was used to start the pump, then at the end of the heating period the 'live' from the pipe stat would also feed back to the boiler and keep it going.

You could get around the pump overrun with a relay that can be set to de-energise several minutes after the boiler went off. obviously the pipe stat would need setting at 80 deg's c or there about's

Untitled

• stem
• 12 Jan 2010
• 3

But then does the permanent 'live' supply any other part of the boiler circuitry that may not function if it was missing such as a frost stat for example.

Pipe stat method for pump over-run , if your boiler manu' allow's it pipe stat has 3 terminal's connsct live from pump to terminal marked C (common) , connect a switch live from system to term , 1 (breaks on temp rise ) , connect a permanant live to other terminal 2 ( make's on temp rise ) boiler & pump switch off , temp in flow pipe rise's on latent heat terminal C-1 break on temp rise C-2 make permanent live pump over-run , temp drop's C-2 break ect ect (simples)

 

[simond]

You can't feed the CH boiler from two supplies without a relay/contactor.

The two power circuits would be joined together when the boiler was on, leading to extra current potentially running through the PCB amongst other things.

The Viessmann 100 Compact can be used without pump overrun, but still needs a perm/switched live. The Kidd Gas series doesn't use pump overrun or switched live but these don't start below £4K.

The way we all get over this problem in the trade is to run the required cabling and charge for it. Customers who don't want to pay can get an installer on a horse who will bodge it up and bank the cash before you find out.

Like many in the trade, I se examples of the latter a few times every year. The installer concerned never answers his phone it seems.