bypass valve to swich off boiler?

[R P McMurphy]

is it possible to modify or buy a central heating bypass valve that will operate a swich that will stop the boiler cycling unecesarly? it will obviously need a delay of say 5 mins on it?

rpm

[Christian McArdle]

You could implement some logic that pulses it every 10 minutes (at least when the programmer is set for CH) to see if it needs to start up again. It would probably need to OR the boiler pump output and a 10-15 minute timed pulse with low duty cycle. (i.e. 5 seconds every 10 minutes). A 555 timer and a low voltage coil relay should suffice, although you may need two relays if the boiler electronics won't let you just wire the timer relay to the pump live. I wonder if someone has already packaged the logic?

So, the controls would consist of TRVs on all radiators. An automatic bypass valve. A flow switch on the heating circuit. No room thermostat.

Zone valves will be connected up Y-plan or S-plan as normal for the system used (no zone valves required for combi or heating only system).

The boiler is set to fire only when flow is detected on the heating circuit (or there is a DHW demand from the zone valve, if applicable). The pump is set to run when the boiler pump output is live, or when the timing device described above is active. The timing device produces 5 second pulses every

10 minutes when the programmer is set to CH On. If flow becomes established, the boiler will fire, which will keep the pump on. The 5 second pulse may need to be extended if the boiler takes time to make the pump output live.

Christian.

[Christian McArdle]

Nah, you just didn't get my reply quick enough!

Although I make the suggestion, I wouldn't say I was the proponent. I favour the programmable room thermostat approach myself, with the house subdivided into multiple zones, at least one per floor.

Christian.

[The Natural Philosopher]

On the other hand, forget all that crap and run the pump all the time the zone timeclock calls for it....:-)

If you are just pumping hot water round a short bypass loop, it isn't going to cool down very quickly...

[The Natural Philosopher]

Oh, so do I. It's just VERY expensive to retrofit, and not that cheap to start with on a new build.

[Christian McArdle]

That is probably one solution, provided you can ensure that the pump overrun will work when the timeclock switches off. Some pumps specifically state that they can do this. However, a pump uses around 100W on full speed. That's a lot of power wasted if it doesn't turn off and no heating is being used.

It won't stay hot for long, provided the flow switch interlock correctly turns off the boiler.

Christian.

[Christian McArdle]

I managed it cheaply on my house. I was lucky enough to notice that the only connections between the upstairs circuit and the downstairs was through the understairs cupboard. I cut the lines and put the zone valves there. Just needed to run a bit of new unzoned 22mm back to complete the circuit. It works so much better than having only a single thermostat. Firstly, the different floors have very different temperature profiles, so a room thermostat in one does not reflect the heating requirement on the other floor. Secondly, having separate timings for bedrooms vs living rooms is excellent.

However, I must remember to put Bedroom 3 on the upstairs zone, it's still on the unzoned piping...

Christian.

[Roger Mills]

I wish I could do that, but I can't. I have solid floors downstairs - so all the heating is distributed between the floors - with individual drops to each downstairs rad, off the same pipes as for upstairs rads!

Roger

[Ed Sirett]

I don't think he meant you, Christian. I think that he probably meant that proponent who advocates. Microbore system because they self balance. Floor-standing thermal storage combis. Grundfoss Alpha pumps.

Essentially the 'smart' bypasses are used on systems where the pump is not controlled by the boiler. The CH demand is taken to the pump but to the boiler via the bypass contacts. The pump keeps running both moving water around and holding the bypass open whilst the boiler cools down.

I also happen to think (a) programmable room stat(s) + some TRVs is a better simpler and cheaper way to fulfil Part L compliant heating control.

[IMM]

Yes, and they do.

Where applicable. And very good they are too. Ever fitted one?

Where applicable. Ever used one? Ask Andy he has.

The point is that the room stat may switch out the system when other parts of the house are calling for heat.

[Ed Sirett]

We had a thread the other day where they did just that, NOT.

No 'cos I not strong enough to get one in my van but I saw on ethat had been leaking for 2 years yeasterday.

No I have not. Mainly because I tend to fit boilers with integral pumps.

[IMM]

Not implemented properly then.

They are made by Bosch. You found one leaking so all must leak. What strange logic. Or was it because it was not a Vaillant, those boilers you go ape over..I did a Google..read on...

I wouldn't have another Vaillant. We had a bugger of a job to get somebody to fix it the first time it broke down. The last time it was impossible. Coulsons even rang Vaillant for me and were told they weren't interested in dealing with out of warranty boilers and had nobody in the area.

So we had it ripped out. It probably only needed a new control board but all the boiler people we spoke to said it had something like 7 such boards and they weren't prepared to keep that many in stock.

Anyway we took some advice on what to get instead and all the boiler people we spoke to all said get a British one. We got a Glow worm and it has been fine.

-- Mike Lewis Chartered Accountant

So, you only go on what you have personal experience of. Once again strange logic.

[IMM]

I did a Goggle..and on 2003-10-28 ....

When you hear some describe microbore systems you would think the manifold is some crucial part without which nothing will work. All it is a plumbing fitting for connecting the 8 and 10 mm pipes to the larger pipes that supply the boiler. [Saving a great number of reducing fitting and Ts]

With the advent of flexible plastic pipework in 15mm the main advantage of microbore is no more. The main use of 8 and 10 mm pipework is now to supply gas fires, IMHO.

-- Ed Sirett - Property maintainer and registered gas fitter.

[Velvet]

Interesting. Luckily for me, I have a standard bore sealed CH system. I'm in the hard water area just south of london. My other half has microbore. He's in the hard water area of cambridgeshire.

Out of the two, both installed around the same time, neither will have had much looking after (one I know to be the case, the other is a probability based on it being rented out for much of its life), guess which one has a faster warm-up time & has never needed flushing, and which one only fitfully heats half the house, and has been flushed repeatedly (no zones/trvs on either).

Velvet

[IMM]

By standard I assume you mean 15mm, which is termed as "small bore". I would not regard you as being lucky.

Please tell.

In a hard water area, a mini or microbore system "must" be a pressurised sealed system. If not you "may" have problems. Also, microbore has a faster warm up time when compared to a small bore system, assuming two identical houses with the same sized boiler. If a microbore system does not perform, it has been designed/installed incorrectly.

[Velvet]

I'm not about to go measure my pipes to find out, so can't say if it is indeed 15 and not 18? mm. Out of the two, it is the microbore which has been repeatedly flushed and is still iffy. I'd say the two houses are pretty near identically sized (in terms of cubic metres and floor areas), though obviously different boilers (one's a combi, one's a 'normal' boiler), though one being a house and one a badly insulated old but large maisonette will make a difference, again it's the reverse to what you'd expect, the badly insulated old maisonette heats up faster - perhaps the double glazing on this cancels out the better insulated walls of the house perhaps (which doesn't have d/g).

Apparently no-one told the designers about the requirement for microbore being sealed system in a h/w area - tis true his has one of those header tanks for the heating system. This wasn't installed by a DIY-er, the whole area was built by a developer and they're all the same.

However, why is this a requirement, given there would be (unless the system's leaking) no way for additional scale to enter the system?

I'm still regarding myself as lucky to have the heating system I have, rather than microbore. Out of the people I know who have had microbore, none of them would ever have it again. Don't hear that from those who have 'normal' bore pipes - similarly my parents have normal bore pipes, with a non-sealed system, and as far as I'm aware it's never had to be flushed in the 25 years they've had it (from newly installed, by my father). Microbore *might* work equally as well as 'standard' stuff

*if* it's designed and installed right.

That's a lot of ifs and maybes for me. Oh, not to mention the fact that standard resists damage by what I can only imagine to be a hoover wielded by an irate person (one of the microbore pipes has a large dent/kink in it at hoover-height which has caused the pipe to no longer be totally circular at that point).

Microbore seems to be a cop-out for the building trade rather than a good thing in its own right. Just my opinion.

Velvet

[IMM]

15mm is approx 1/2". the next size up is 22mm (3/4") Microbore is soft coperr of 6mm, 8mm, 10mm, 12mm.

If it has been flushed pout then it maybe drawing in air and sludging up. Bad design/installation.

A combi is roughly twice the output of a "nbormal" boiler. tyhey heat up v fast. this mat be clouding your impression.

They should have made it a sealed system. It may be worth flushing out the microbore system and converting it to a sealed one. Not very difficult.

In theory, an open vented microbore system with inhibitor should give no problems. The problems arise when there is a leak and the water is constantly replenished. Also inhibitor should replaced every 3-5 years on any system.

Millions of microbore system have been installed with no problems whatsoever. You need to have someone who knows what he is doing.

Depends if it has been installed correctly. A relative was sucking air in for the first 5 years before I rectified the installation problem. Subsequently the rads all rotted.

After 25 years and no inhibitor replenishment, the rads are probably on their way out. Convert it to a sealed system and see all the rads pop.

Poor installation. The pipe should have been above damage height.

Yon should learn more about it. In soft water areas it is the norm and the heating engineers there know you it works, how to install it correctly and get the best from it.

I think you mean, you would not have it as the installers around you don't know about it.

[Christian McArdle]

Um. I've NEVER seen a house with suspended floors where the radiator pipes don't normally go down into the floor. You can't avoid hoover height. You can only install something man enough to resist it. If I had to have microbore, I'd still like that last 20cm done in chromed 15mm pipe from below the floor to the TRV/lockshield for aesthetic reasons.

Christian.

[Velvet]

Bit of a damage-prone way to find out, isn't it? ;-)

Um, how, exactly, when the pipe runs under floorboards (upstairs floor)?

No, I mean that if I have a system that I have seen working for donkeys years, why should I have something that may or may not, regardless of the competancy of the engineers who design and install it, work... far easier to go with something I have had experience of working without hitches ;)

Velvet

[Velvet]

Exactly. Which (unfortunately, IMM) makes me wonder just how knowledgable IMM is regarding this. I can't believe someone that knows microbore inside out and back to front hasn't ever come across the situation where pipes exit floorboards up to the radiator on the wall.

Anyway, moot point, since given experiences thus far I'm still no closer to changing my mind, and any place I wind up in will either have standard bore or will be bought with the intention of removing whatever else is in there to *have* standard bore put in (ie, some place needing a LOT of work done on it).

Velvet