Yes, depending on the type of boiler used. If you have a natural draught boiler the fuel efficiency will be poor compared to a system with a thermostat and TRVs.
The difference will be less marked on a modern boiler.
Removing short cycling is desirable. To do this you need to get the TRVs to do a little less restricting and the wall thermostat to cut a little earlier.
Thanks Ed. Am I right that this would mean lower temperature at the hall, but potentially higher temperature in the bedrooms?
Also, given that the lounge temp is (undesirably) lower than the rest of the house (because the room stat at the hall cuts out before the lounge has warmed up), won't the lounge now be even colder?
And finally, were we effectively contributing to short-cycling when restricting heating at the hall radiator, where the room stat is also located?
Yes, I was thinking along those lines too. Even with the room stat temp reduced down from 21.5 to 21, it seems to me it cycles on for 1 minute every 10 minutes. Yep, the default cycle rate is 6 per hour.
So, Ed, if we substantiate that it kicks in every 10 minutes for 1 minute, does this count as short-cycling for a Potterton Netaheat? If yes, I can reduce the cycle rate to 3 per hour or increase the minimum time it's on. With the current settings, if the room stat indication is anything to go by, it can maintain 21.5 (and 21) with no probs.
Thanks again,
Kostas
OK now we have some real data to go on. The actual heating load is about 10% of the boiler's output which is probably about 20kW so 2kW. That's probably why the lounge is too cold. You need to get the lounge rads hotter and/or have more of them so that the boiler has a better opportunity to heat the house. In the recent weather 2 kW is nowhere near enough to heat a house.
If I have read your posts correctly you have the following symptoms.
1) The thermostat cuts in the hall too early before the lounge (and maybe elsewhere has warmed up). 2) If the thermostat is turned up the boiler simply short cycles at about 2kW with a warm hall.Taking this altogether suggest there are sizing and/or balancing issues. Especially that the hall radiator is working better than required and the lounge ones are not doing a good enough job.
With the boiler set to medium/ medium-high the lounge radiators should be hot if they aren't then the problems lie with balancing and/or sludge and/or primary flow problems. If the lounge rads are hot then the problem lies with insufficient lounge rads and/or draught proofing issues in there.
You need to throttle the hall radiator back. Finally bear in mind that although a Netaheat is a fairly reasonable boiler (especially for its time) you can't get the sort of efficienc you can get out of contemporary kit.
Ah! Tuning CH.. This seems to be a lifetimes work, or at least I seem to have been doing it in one way or another since having central heating installed in our first purchased property in 1963. Now, many homes later, I too am just switching over from a Honeywell CM67 to a CM927 in an effort to better control the heating in this house. Various professional heating engineers and a lot of DIY have taken place in the intervening years and there have been quite a lot of technology changes but it is still a bit of a black art and I doubt if I will ever be totally satisfied.. Scientifically if the radiator sizes have been correctly calculated you could measure the temperature differences across each radiator and come up with a sort of 'balance'. But what worked on one day (when the engineer or I did it) would not work for certain on another day when the sun was perhaps blasting through double glazing and a patio door or a cold east wind (like today) was blowing on the wall where the thermostat was located and artificially calling for more heat. The CM 67 has been there for six years or so and was definitely an improvement on the original Satchwell stat that was situated next to the boiler cupboard on the wall next to the north facing back door. It was great at keeping that passage warm but of course clicked on if anyone went to the garden or dustbin during winter months.. The programmable stat was installed in the living room on an inner wall between the room and the easterly facing roofspace. We soon discovered that that roofspace gets very cold in dull cold conditions and with any East wind and this played havoc with the CH tuning.. Fortunately East winds are fairly rare here (summer dry spells are no problem). Normal south-westerly cause next to no problem but a low winter sun on another patio window can get to the thermostat and make the house very cold on a chilly but very bright winter's day.. Hence the switch to the CM927 this week to and a move of the thermostat to an internal wall or bookshelf.. (Its actually sitting there now though not controlling the heating as I have to rewire the live/neutral to the wiring centre to the get the 927's receiver/relaybox to work) So it goes on and I guess I will never be entirely satisfied though with the promised global warming perhaps it will be much less of a concern in the future. I've come to the conclusion that it would be best to live in a subterranean house with little in the way of external influences from sun, wind and rain. But then I would lose my views of the sea! I am sure others may have had the same experiences. Michael in Sussex
"Ed Sirett" wrote in message news:fhkjkl$fh6$3$ snipped-for-privacy@news.demon.co.uk...
It's only the lounge that lags behind. The other rooms heat up to at least the same temp as the hall.
I think it's probably as follows:
"After the hall reaches the desired temp, it drives the boiler at a fixed frequency (10 mins) and for 1-2 minutes each time".
A later experiment will be to reduce the CM907 setting for number of cycles per hour.
So, the boiler is set to 3 (indications are min 1 2 3 4 max) and the lounge rads get hot. It is clear that if I throttle the hall, the lounge can get to 21.5 (which is probably more than necessary; I am tempted to reduce the room-stat target temperature as soon as I can achieve it at the same time throughout the house.)
I am working on that, thanks to your suggestions. 4-5 days ago I was
11 quarter-turns from shutting it off, now I am 7 to go. I am trying to converge to a reasonable setting.If I achieve all that it will be down to your persistent advice, Ed.
Kostas
OK you have a normal rad valve that's about 3 turns. In my experience there will be no effect on the heating until you are down to 3 or 4 quarter turns from closed.
If I suspect and/or receive information that the thermostat area (often a hall) is easily over heated then I do this: I fit a TRV, but I use the anti-tamper pins to fix it at the setting I believe/discover is the right for the system. I will of course have to make a return visit to check that it is well but I have the ability to fine tune the heating system.
What's more the effect of the other TRVs will be to work against your efforts on the hall rad.
That's very interesting. I thought you are not meant to have a TRV at the same place as the room thermostat. I believe I read it on the Honeywell site.
The hall has two rads. One is a single, vented with a TRV (set to 0) and the other is a double, double-vented without TRV that I am trying to use to tune the system. The single one is further from the room stat and closer to the door.
Another avenue to experiment with (but I will have to come back to ask how to set the anti-tamper pins on an old Honeywell TRV :-) ).
Thanks!
Kostas
The ideal design (IMHO) is that the entrance area should be a little under heated and contain a radiator with no TRV. The programmable thermostat should be easily accessible yet not subject to solar gains nor too close to the radiator. This allows the prog stat to be easily set to the "we are out" " we are in" settings if that's how your life style requires. All other radiators are adequately sized (over sized if condensing boiler) and controlled by TRVs.
In the typical world we have to make compromises to see what we can get from what we've got with as little effort as possible.
OKay.... why don't you turn off the big one and then start experiments with the TRV setting on the little one!
No idea.
Just to close this thread: the method to throttle back the radiator has worked. I am now happy with the heating in the lounge. Many thanks to Ed and everyone who has contributed to this thread.
Kostas
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