Dodgy Boiler Installation - More advice requested please!

[ricarbo]

I'd had a look at the Potterton info on the web before making my comment about the interlock. I thought I saw, on the page describing the boiler operation, something about it having to 'prove' flow for 2 minutes, before firing. If I misread it, my apologies.
Concerning the bypass, my understanding is it needs to be automatic and the web info didn't make it clear if the internal bypass is constant or auto, I think. So I'd ask Potterton for clarification, on both points, if I was Barbusa.

 

[Paul Barker]

I am sure that the internal bipass is constant, but that is outside the fitters control, different rules would apply to manufacturers, they may well find themselves having to make it auto in the future. The point is that as long as the boiiler is protected by a bipass and the manufacturer says an external bipass is not therefore a requirement of theirs then there is no need to fit a bipass. True that if you do fit one it must be an auto one so that it is energy efficient.

Adding an auto one because the internal one is not auto will make no difference to energy saving whatsoever....

They can only save energy if they are the only bipass.

I still think that a rad controlled only by roomstat is the best method. I have no problem with making this such that it cannot be controlled by the user, i.e. correctly size it, balance it under the floor on installation, connect up to it with 1/2 inch male iron.

You might have gathered I don't like bipasses when no need for them.

 

[Agile]

Paul. as far as I am aware ALL boiler bypasses are auto. This is achieved by using a spring loaded valve which needs a few meters head before it opens.

Ricarbo, I suspect you were looking at the Performa HE which may be one which proves the flow first before providing CH.

Tony

 

[croydoncorgi]

There seems to be a lot of confusion about the purpose(s) of a bypass, automatic or otherwise.

Unless something has changed, they are ONLY needed to provide a path for circulation in the system to dump excess heat from the boiler in an overrun condition (ie. AFTER the burner has been switched off but BEFORE the heat exchanger has cooled).

To do any good, a bypass has to be 'some distance' from where the heat is, otherwise there won't be any chance of the heat dissipating. Some manufacturers specify a MINIMUM distance. I can't see any particular reason for a maximum distance.

If a bypass is open with the burner on (because the system design is c**p or because it's a gate valve!), hot Flow water will 'short-circuit' back to the boiler.

In conventional boilers that may not be TOO much of a problem: all that will happen is that the boiler will get hotter and the internal thermostat will shut off the burner. In the worst case, the rest of the system will not get hot enough and the house will never heat up - but that would be pretty unusual.

But with a condensing boiler, recirculating hot water back to the boiler is the LAST thing you want! A MAJOR OBJECTIVE of design in energy efficient systems is to MINIMISE Return temperature. Otherwise the boiler CANNOT condense!!!

If anyone disagrees or doesn't understand, raise your hand now

 

[Paul Barker]

Yes that's why I was thinking in terms of putinmg this wretched bipass beneath the rstat controlled rad, to get it well away from the boiler, hence sufficient pipe run for it to do it's work.

I still don't like systems that require one.

At home I am happy to say I have no need of a bipass because the rads are correctly sized balanced and rstat controlled. No need for useless trv's either, and since I haven't made any major changes since 1970 I am not forced by any government to make said unnecessary and fuel inefficient changes (on the basis of the waste and production using up precious resources).

The most energy efficient heating system is the one that doesn't use up the plantets resources to resmelt metal every 10 to 15 years.

 

[oilman]

Just so you don't get wound up and lose sight of the bigger picture, the government DOES NOT GIVE A STUFF FOR ENERGY EFFICIENCY!!!

It (well the gorgeous Margaret Beckett, sex symbol of the front benches) has decided that tallow (the product of rendering carcases at slaughter houses) is to be classified as waste. Every other country in Europe is happy to classify it as fuel. "So what?" you ask, well tallow is a bio-fuel largely formed by animals from eating grass. This means it is carbon neutral and just the sort of thing that Beckett's boss, Adonis Bliar, has just decreed must make up 5% of vehicle fuels. Tallow is quite handy as it can be used to render the next carcass , releasing tallow and so on saving huge amounts of fossil fuels. No longer, it will be waste and will have to be buried or incinerated , no doubt using fossil fuel.

So give up worrying about efficiency, turn down the stat, put on a jumper, and get used to not being able to afford heating fuel in a few years time. Just remember, the government doesn't give a stuff.

 

[Paul Barker]

Well I'm sat happily infront of my open fire burning free pallets that pts are delighted I remove for them. My builder mate has just bought a log burning stove, he too has in inexaustible supply of pallets.

Don't tell everyone.

Old Amos says, cut your own wood, you warm yourself twice. I would add live longer through staying fit. Also you enjoy the resultant heat a great deal more than sat like a couch potato in front of a dangerous (probably if the many I get to see in my work are anything to go by) gas fire.

 

[ricarbo]

Phew! Quite a few viewpoints!
The tallow story is amazing!
Yes Tony, I was probably looking at the wrong thing.
Back to the bypass - It's not only needed for boiler overrun. If all TRV's shut before the roomstat (which may not exist), then the boiler will probably lockout on overheat as it will still be firing when the flow stops.
On commercial installations, it's done differently - Typically there's a loop which has a pump (the primary pump) connecting the flow and return of the boiler (a permanent, fixed bypass circuit, not automatic). Boiler firing is controlled by the return temp, not the flow temp (but that can interrupt the firing if too high, to prevent overheat). Then there's a three port valve(s), with proportional control to open up a route out of this primary loop, supplying a secondary loop(s) round the building with further pump(s), (the secondary pump(s)).
The temperature sensors in the heated space(s) control the proportional valve(s), so each secondary loop gets just enough heat. Rather complicated for a relatively small domestic installation, so not economic, but allegedly highly efficient. I'm not sure if they use condensing boilers, but get efficiencies in the high 90's. The losses in the primary loop are minimal because it's short and well insulated.
The shortcoming of a roomstat controlled domestic system is that you have to heat the room the 'stat is in, even if you don't want to use it today.
I don't know what the best answer is. Technically, it's probably with more electronics, but you soon reach the point that it's not economically efficient to incur the installation costs, particularly on an existing building, which is of course the vast majority of installations. Personally, I like the idea of TRV's throughout, with a flow switch in the heating circuit to stop the firing when they all shut, but it needs electonics to allow the pump to prove flow and then enable firing. I believe the programmable thermostat comes from research in Germany which showed people were opening their windows in the afternoon, because they got too hot!

 

[oilman]

The shortcoming of a roomstat controlled domestic system is that you have to heat the room the 'stat is in, even if you don't want to use it today.

That's why it's normally in the hall, and the temperature is set lower than the sitting room would be.