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

[Doctor Drivel]

If that is a problem a simple outside stat set to 20-22C will prevent all that.

Stopped. If on the time clock then the burner is switch off too.

[Christian McArdle]

I'm not sure if that would be OK. I believe the call for heat is based on the room temperature within the zone, not on outside temperature.

Indeed. But that is not an interlock based on the call for heat for the individual heating zone.

Let's face it, a flow switch is a much more reliable and compliant installation than a difficult to debug differential temperature based system.

Christian.

[John Rumm]

Probably not (at least not for that reason), but it would depend on where it was and how it was routed. Under a kitchen floor or in ceiling space would usually be fine. Chased into a wall it might count since it would need to follow the allowed cable zones - and this can and does pose a potential risk if not done correctly - more so in a bathroom / kitchen.

[John Rumm]

LOL...

this is classic Drivel - start with a dodgy bit of design. Kludge loads of extra kit on to it each time people identify holes in the original design. Keep going until you have a massivly complex arrangement that still does not meet the actual requirements and costs way more (in both time and money) to implement than doing it the right way in the first place.

That ain't the same as an interlock - it need to work when the time switch says "run", but the actual house temperature is warm enough without any further heating.

[Doctor Drivel]

pat-n-dave, do you think you are trend in your new Essex Chav clothes?

[Doctor Drivel]

The idea is to stop the burner. An outside stat caters for high temp stops during the day. Cool in the morning warm during the day, so burner (and pump) off

Firstly you need to install a mechanical valve (drain down etc). The flow switch requires the pump to operate full time. If all TRVs are closed the pump opens up the auto by-pass. and give boiler flow and mechanism to detect if there is flow with the flow switch which is on the CH rad circuit away from the by-pass loop. It will work. With a system boiler where the boiler controls the pump you may need a timer to test the flow by operating every 2 mins or so; if flow operate, if none stay off (more complexity).

A couple of stats can do the same thing and save money in operating costs too. On a condensing boiler it can also feed the boiler with a low return temp improving efficiency. It just means you have to design and balance the system properly.

[Rob Summers]

Thanks muchly for that information that could well have saved me quite a bit of cash.

Rob

[Christian McArdle]

It against building regulations, as it can still provide burner operation when there is no call for heat. There is frequently no call for heat with an outside air temperature of 20C. Clearly a proper interlock system will provide better operating costs.

It would also be very temperemental. As the pump wears out, it might provide a different speed/pressure, so the differential temperature will change. The return temperature may respond oddly to changes in conditions. All in all the system sounds completely impractical and over complicated.

Christian.

[Doctor Drivel]

You could say that about an integrated thermal store. No call for heat yet the burner is running heating a cylinder. Lag the flow, return and the by-pass pipes and you are in the same situation.

So, the outside stat saves energy, and a lot too

This is one.

It will not be temperamental at all.

Over complicated? Two stats and some lagging? Get real. What wastes energy is the standard interlock of stat in the hall with no TRV on the rad. People overset the hall wall stat so the rest of the house is warm, as the hall is not representative of the whole house. The coldest and draftiest room in the house then has too much heat pumped into it wasting energy.

I put a pipe stat on the return of a relatives system which doesn't have TRVs and an old cast-iron boiler. It stopped a hell of a lot of cycling and promoted efficiency as lower temps are generally more efficient. I set the pipe stat on the boiler CH return to 58C so the boiler never condenses. The garage wall behind was north so I fitted a stat in a box outside set to 21C. They installed Double glazing and 1 foot of insulation in the loft so a flow temp of 70C was fine. The fuel bills went down noticeably, all because of a few stat. It now has a new condensing boiler.

[Christian McArdle]

What is complicated is the control logic, as simply relying directly on the return temperature will provide weird operation without some processing.

Yes. I hate the idea of having it in the hall. This is why my house currently has 3 heating zones, with another 2 to come. The stats are in the most frequently used (or only) rooms in the zone, so provide optimal comfort in the right place.

Christian.

[Doctor Drivel]

It will not. When it comes back hot the house is up to temp. Simple. You balance the system to suit, which should be done anyway.

[Roger]

The message from "Doctor Drivel" contains these words:

That might be the case in your hovel Drivel but more adequately designed houses would have a vestibule which would make the hall the least drafty room in the house. Never the less as you might just recall I am a firm advocate of putting the room thermostat in the living room if that room does not have a supplementary heating source.

And no my hovel doesn't have a hall. It wasn't considered necessary in peasants accommodation hundreds of years ago.

[Doctor Drivel]

"Roger" wrote overt Rogerness in message news: [e-mail]...

** snip Rogerness **

His new Essex Chav clothes for Xmas are getting the best of him. I bet he bought a white van to one of the boys too. Sad but true.