Part L certificate - what is it?

moneysavingplumber

gromituk wrote:

The only way a room stat can possibly make any sense is if it is located in the coldest part of the house, and you can only ensure that by making sure there are no opening windows elsewhere, and none of the radiators elsewhere can be turned off!

What is needed, instead, is for the pump to come on periodically and the flow/resistance to be measured to determine if any TRVs are calling for heat.

The cylinder stat is a different matter, because it controls a valve which actually controls the temperature it's measuring, and has no other consequences.

This goes against almost all professionals' opinions that I know and speak to and government research and guidelines (including Energy Saving Trust documents), and my own experience does not concur with what you say. The room stat needs to be located in a room that reflects the average temperature of the house, preferably in a downstairs living space, away from drafts and obvious heat sources.

Pumps are wired from the boiler, not the other way around. The by-pass itself acts to adjust to pressure changes, if you eliminated this in order to facilitate your proposals, there would be system noise everytime the pump met TRV resistance, you would also have overheat problems and scale build-up on most modern boilers.

The room stat is the pivotal room temperature control point of a central heating system and always has been, builders posing as plumbers have for years been using TRVs thinking of them as an alternative, but they have never been intended by the industry to be an alternative to a room stat, but as a compliment to it. The idea of TRVs is to perhaps cool off rooms where heat isn't required and to adjust where the sizing process or heat loss values of a room may have been overestimated, it allows fine-tune adjustment that you can periodically change at will, without the wear that you would get on a traditional valve. The TRV has never been intended to be an overall temperature control on a domestic heating system.

The room stat also controls a zone valve and is no different to a cylinder stat in that sense. The valve motors and turns a microswitch which fires the boiler which then sends power out to the pump.

In larger properties there should be 'zones' controlled by individual room stats.

Best Practices HR6 and HC6 actually recommend programmable room stats on each zone.

Ultimately, whether you like it or not, it is part of the requirement under Benchmark and Part L that boiler interlock be provided by way of a room thermostat and programmer at the least.

moneysavingplumber

invisiblegirls wrote:

My heat exchanger has just been leaking.(Stelrad Ideal)
Turn off the electric, gas and water. Drain down
4 Pieces of stud iron to seperate the heat exchanger in two.
4 'o' rings to re seal the leak.
Put back together.
Check the o rings are available first they are hard to find and are not just ordinary ones.
HTH

Most heat exchanger leaks are due to corrosion actually damaging the metal itself. This isn't the sort of work that should be done by DIY, it will usually interrupt the 'gas train', especially on a room-sealed boiler, making it a contavention of gas safety regulations if carried out by somebody not legally deemed to competent, i.e. Corgi registered.

gromituk

moneysavingplumber wrote:

The room stat needs to be located in a room that reflects the average temperature of the house, preferably in a downstairs living space, away from drafts and obvious heat sources.

And this is where I think it is a ghastly compromise.

1) What if you want to heat up another room (because there's been a window open, or because you don't heat all rooms all the time, say), and the room stat is not calling for heat? Your heating system is switched off, so you can't.

2) What if you decide to turn the radiator off in the room with the stat? The stat will call for heat constantly - it will be pointless.

These documents must assume that you want to heat all the house all the time and leave all the internal doors open, in which case the room stat might have some use. I don't do that - I have quite a big house with two people living in it. I save an awful lot of energy by using the heating selectively.

The by-pass itself acts to adjust to pressure changes, if you eliminated this in order to facilitate your proposals, there would be system noise everytime the pump met TRV resistance, you would also have overheat problems and scale build-up on most modern boilers.

Yes - you're right. What you could do is have an automatic bypass with a switch to it which is activated when it needs to open far enough to pass nearly all the flow from the boiler. Bingo, that's your resistance measurement done for you, and hence your temperature measurement taking into account every room, which you cannot do with a room stat. If this switch is activated, the boiler and pump stop for a few minutes before trying again. Or perhaps the boiler stops and the pump slows right down, so that it can monitor the TRVs continuously via another, lower pressure, switch? Now how can that possibly not be at least as effective as a room stat?

The room stat is the pivotal room temperature control point of a central heating system and always has been,

Well it used to be the only room temperature control point, and I think far too much emphasis is being placed on it for historical reasons; now with TRVs I am suggesting that it is a really sub-optimal form of control. I can understand that you don't want the boiler on when heat is not required, but a room stat cannot ascertain this situation accurately, as I explained above. Your TRVs can, but without some further means of control they will cause the boiler to short-cycle.

The room stat also controls a zone valve and is no different to a cylinder stat in that sense. The valve motors and turns a microswitch which fires the boiler which then sends power out to the pump.

Yes, I know exactly how it works (in fact with traditional systems the boiler doesn't control the pump - the valve/thermostats/programmer control both in parallel). But I have explained above why the cylinder stat is a much more sensible thing. It actually controls something which affects the temperature of what it is measuring, and nothing else. A room stat on a whole heating system does not.

In larger properties there should be 'zones' contolled by individual room stats.
Best Practices HR6 and HC6 actually recommend programmable room stats on each zone.

Well there you go - a rather expensive alternative to what I am proposing, which requires no zone valves, extra plumbing, or extra thermostats at all! Just a rather more sophisticated bypass valve (shouldn't cost more than one zone valve) and a rather cleverer control system (very little cost).

Ultimately, whether you like it or not, it is part of the requirement under Benchmark and Part L that boiler interlock be provided by way of a room thermostat and programmer at the least.

Would they accept my alternative, I wonder?

moneysavingplumber

gromituk wrote:

Yes, I know exactly how it works (in fact with traditional systems the boiler doesn't control the pump - the valve/thermostats/programmer control both in parallel).

Very few modern low-content boilers now operate without pump over-run, which requires the pump running for around 8 minutes after the boiler has gone out, and which operates regardless of stat and programmer settings, to dissipate residual heat from the boiler, and requires the pump to be wired direct from the boiler.

gromituk wrote:

Would they accept my alternative, I wonder?

At the moment of course they wouldn't, but if you think you have a viable alternative I would suggest you develop it, patent it, and get yourself on The Dragons Den on BBC2 and see if they like it!

gromituk

I know about pump overruns - remember I mentioned them in when talking about my Netaheat? The only reason for one for that boiler is to stop the overheat stat tripping, itself only required for sealed systems. Because modern boilers already control the pump electronically, it would not incur a large cost to add the control system necessary to implement my proposal.

I can't patent it - it's now in the public domain!

But what do you think about the idea? I'm sure there must be problems with it but I'd be keen to know what.

moneysavingplumber

Well it wouldn't surprise me if something along those lines hadn't been investigated by big name companies already, it sounds interesting but it would take a greater mind than mine to pick it apart fully! I'm always interested in debate and views and alternatives, but of course the OP has to come first on this forum, which is what I have tried to focus on.

The government's ultimate concern seems to be fuel, which is why the boiler interlock is so important. Boilers like the Alpha already incorporate daily pump kick, but I assume you're suggesting a pump kick every fifteen minutes or so, with a resistance meter of some kind that will sense a reduction in resistance and then switch to activate pump, zone valve and boiler fully until resistance has recurred. It does sound interesting, although some egghead Tefal type is bound to point out some glaring flaw just as you're getting extremely excited about it!

economiser

I agree gromituk about the thermostat position. I removed my room thermostat years ago because it was in the main living room. We have an open log fire, plenty of free wood around here, and of course when this was in use the rest of the house went cold. We could correct this be resetting to a higher temperature but that rather negates the whole point of having it, just another thing to go wrong.

moneysavingplumber

This might interest you gromituk http://www.cm-zone.com/application.php?language=en . An associate that uses the IPHE members' technical forum seems to think you owe him some money as he thought of that himself, but he can't remember when or where :snow_laug .

Just a point about room stat location, if circumstances change and a heat source is introduced close to it, the advantage of the wireless room stats is they can be easily relocated. They are not a perfect answer, but short of a complicated system like the above-mentioned CM-Zoning from Honeywell (which is bound to be expensive), there is still no widely available answer to the problem of boiler interlock, and whilst I accept the system is not perfect, it is still better to have a well-positioned room stat than to not have one at all.

gromituk

Dreadful broken website but I eventually managed to find out what they are from another site, and expensive it is - the valves cost £70 each.

I don't know if there are any bypass valves with sensors, but underfloor heating systems sometimes seem to have flow rate sensors.