New Boiler = Room Stat = Part 'P' & Part 'L' question (long)

[.]

mechanically protected you say ?

perhaps behind a 22mm gas pipe behind a skirting board which has already been passed by a BCO ? see where I'm going ? quick, dirty yet within the regs :D

[Tim S]

Hi

I'm pretty sure you can do what you like with ELV. Consider HiFi cables and burglar alarm wiring - stuff goes everywhere. Ditto CAT5 (though I was naughty and stuffed ISDN down it for a time, and that's not ELV).

Cheers

Tim

[Tim S]

Your BiL is definately wrong, unless there is some other mechanism to cut off the boiler when there is no call for heat. The TRVs can't control the boiler directly unless they are very fancy.

On the subject of the Honeywell RF units, are you aware that they also do an RF TRV head as a more obscure part of the range?

I've toyed with that idea, makes multiple zoning a doddle (and reconfigurable). You might get some benefit by replacing the odd TRV in certain key areas piecemeal over the course of time.

ie if you fitted the RF roomstat and receiver it leaves the possibility to add more roomstats and TRVs later.

There might be something about ELV in special locations (kitchen, bathroom, with telecomms excepted) and part P, but I wouldn;t worry too much about it (personal opinion). Part L, well, IMO do what you like. If it ever becomes a "problem" it's not going to be very expensive to "rectify" it in this case. Your local BCO's probably got more to worry about than your boiler controls.

HTH

Tim

[Andrew Gabriel]

Also, there is no exemption from Prat P for extra low voltage wiring (which is I presume what you mean, as mains wiring is "low voltage").

[Hugo Nebula]

On Tue, 03 Jan 2006 15:24:21 GMT, a particular chimpanzee named "." randomly hit the keyboard and produced:

In relation to Part P; strictly speaking, any electrical work in the kitchen is controlled. However, if your installer is CORGI registered, he is exempt from giving notice provided the installation is, "as a necessary adjunct to or arising out of other work being carried out by the registered person".

WRT Part L; the installation of a central heating boiler is controlled, but once again, if the installer is CORGI registered, he is exempt from giving a notice. The work to replace the boiler would include for upgrading controls.

[legin]

Why not just fit the stat next to the boiler, that complies, no worrying over cable runs!!

[.]

that's just the sort of information I was seeking, thank you.

in relation to the Part P bit, would pulling a single, unbroken, cable /through/ a kitchen be classed as work /in/ the kitchen ?

thanks again.

[.]

is what BiL said but I've got the cable from stock and the stat really ought to be in the living room, soooooo, if I could pull the cable along the route laid out in my original post, it would be no more difficult than siting the stat in the utility room. 12m cable and a hand full of clips, I've got a bag of one coat plaster and some spare capping.......

there's cutting corners and there's bodging. it's a fine line :-)

[Dave Liquorice]

Isn't there? You mean you can't DIY a battery operated doorbell any more? ISTR a recent thread about this some where that concluded that stuff like ethernet etc was excluded but phone lines weren't as ringing was above the voltage levels that defined the Part P cut off.

[Ed Sirett]

Generally the wiring is at mains voltage.

[Doctor Drivel]

Via the pipe stat.

The pump is always on. Lag the return pipe around the pipe stat too.

If the temp drops below 71C the system requires more heat and the pipe stat brings on the burner. The design is 10C across boiler and rads with 80C flow temp. If the 10C differential narrows (higher return temp than 71C) the house has warmed up, so the burner is switched off. An interlock that detects when the house has reached temperature.

If the TRVs close up and the by-pass valve opens the return temp will rise above 71C, then the burner will be switched off. The house cools and some TRVs open and a flow of water goes to the rads dropping the return below

71C, then the burner switches in.

If the design is 70C flow with 22C across the rads and and boiler then set the pipe stat to 49 or 50C. It then ensures condensing at all times, and no by-pass returning 75-80C water back through the return and lowering efficiency, and ensures the flow temp to the rads is low.

[Set Square]

But as someone else has pointed out, there is a major falicy here - and the boiler will cycle. As soon as the return *pipe* falls below 71C, the boiler will fire again. It doesn't require the *house* to cool and a TRV to open. So it won't satisfy Part L. Or are you suggesting keeping the pump running all the time? - in which case you'll waste a lot of electrical energy. Even so, the boiler will still needlessly heat the water to 71C in mid summer!

[Doctor Drivel]

That is what I said

Not much at all. You could have another stat set 3 degrees above to switch out the pump.

Nope. If the return cools the house has dropped in temp and/or the TVRs have opened.

[Andrew Gabriel]

This fails to comply with Part L. Such a scheme would need to use a flow switch to detected all zone valves closed and keep the boiler off.

[Doctor Drivel]

Part L says an 'interlock'.

[Andrew Gabriel]

Which is precisely the bit you're missing.

Your scheme keeps the boiler and bypass loop maintained at

80C when no heat is required. Part L requires the boiler to be switched off when no heat is required. This is to avoid the energy wasted in keeping the boiler and pipework up to temperature when there's no demand for heat.

[chris French]

No that wouldn't be mechanically protected - it needs to be in steel conduit, or covered with suitable steel plate

[Tim S]

Having just conferred with someone on the IEE forums, there is another option, which is to use a cable with an earthed screen designed to provide protection in the event of being punctured by a conductive object.

Specific cables which are quoted as OK to run outside of the permitted zones are Lapp XL-Shield and FP200.

XL-Shield is interesting stuff - earth core which remains in contact with a foil screen along the entire length of the cable. No special termination techniques or fittings needed. Details here:

is more common, though, being used in fire systems. I'm not sure if it required special termination.

Both types are fiendishly expensive (1-1.50 per metre), friendly trade counter might sell it cut.

HTH

Tim

[Christian McArdle]

Bollocks.

Say the outside temperature is 30C. The rads require no heat, therefore the return temp drops below 71C. What prevents the boiler firing?

The answer is nothing. The boiler will fire. It will heat the primary circuit, wasting energy and it WILL NOT comply with Part L1.

There is nothing in your scheme that prevents the boiler firing if the house is hot. OK, there is something to stop the boiler firing if the house is hot AND the system is already running. However, if the system has stopped and cooled down, then it will restart, cycling forever, despite there being no call for heat at all.

Christian.

[.]

Outstanding example of the glory of usenet !

many thanks Tim