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Landshark2007
Junior Member
Joined: 15 Nov 2008
Posts: 4
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 Posted: Sat Nov 15, 2008 11:41 am Post subject: Central Heating nightmare |
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OK, I am sure that this has been asked many times before, but please bear with me.
I have a combi boiler in the garage which is linked to the controller in the hallway with the only thermostat. All the radiators are fitted with valve thermostats and all work well.
Problem is simple. When the hallway is at the temperature set on the thermostat, the boiler cuts out (as it should do). The rest of the rooms in the house get colder and colder as the heat drifts away, but since the hallway remains warm, the boiler does not cut in. Having turned off the hallway radiator to try and reverse the problem, I am then faced with exactly the opposite whereby the house then becomes a furnace as the hallway remains cold until you physically go and turn the thing off.
What I want is a set of multi-room wireless thermostats that can control the boiler call for heat - anyone have any ideas please as this is driving me nuts!?  |
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Sat Nov 15, 2008 1:00 pm Post subject: |
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I was trying to think without success, to think of someone I know that actually shuts the Lounge doors when they're sat in it. 
You could restrict the heat into the hall rad by turning the lockshield valve down, but the lunge should be controlled by the TRV if they are working properly, the house shouldn't become a furnace, that says to me the trvs are not working or adjusted.
You could fit a programmable wireless room stat, but to fit more than one you would need to zone the system.
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Stoday
Electricity economics consultant
Joined: 20 Jan 2006
Posts: 3227
Location: Sitting on the Bog
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| Posted: Sat Nov 15, 2008 1:58 pm Post subject: |
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An alternative to zoning is to control each radiator with its own valve controlled by a programmable thermostat. Unlike most valves this one is small and neat enough to go in a living room.
Click Here
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Steve the Gas
Senior Member
Joined: 30 May 2008
Posts: 794
Location: Notts/Derbys
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| Posted: Sat Nov 15, 2008 5:03 pm Post subject: |
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It don't look great  |
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Landshark2007
Junior Member
Joined: 15 Nov 2008
Posts: 4
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| Posted: Sat Nov 15, 2008 9:35 pm Post subject: |
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Thank you for the replies. The fundamental issue is that the heating system design is fundamentally wrong as the base assumption is that no-one shuts doors. If this was the case, then the design would work, however even then it is also flawed.
A heating system whereby the only 'call for heat' is made by an electronic thermostat set in the wrong place by the installers means that no room is going to ever be warmer than the hallway.
My idea was to have a wireless thermostat in each room. Set the system up and then crank the boiler to full whack with all the doors closed and all radiators shut off. You then take each room up by opening the radiator themostat valves until you reach the displayed temperature on the wireless sender. You repeat this for each room and voila you have a home that will only demand heat for the rooms that you have the controller set up for and with other radiators that will not be affected if another thermostat makes the demand.
The logic and the setup is sound - the problem is that I cannot find such a thermostatic system in the UK. |
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Sat Nov 15, 2008 9:55 pm Post subject: |
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| Landshark2007 wrote: |
| A heating system whereby the only 'call for heat' is made by an electronic thermostat set in the wrong place by the installers means that no room is going to ever be warmer than the hallway. |
Sorry that is not correct, the radiators distribute the heat, and the room stat only senses the air temperature.
For multiple room stats, you should look at the link Stoday posted.
Wirsbo Digistats and control centers we use for underfloor heating will do the same job
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Stoday
Electricity economics consultant
Joined: 20 Jan 2006
Posts: 3227
Location: Sitting on the Bog
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| Posted: Sun Nov 16, 2008 6:15 am Post subject: |
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| Landshark2007 wrote: |
| The logic and the setup is sound - the problem is that I cannot find such a thermostatic system in the UK. |
I'm sorry, but your logic is not sound and it won't work. That's why you can't find such a system.
To understand why it won't work, you have to understand how a Thermostatic Radiator Valve (TRV) works.
Just about the worst place to position a thermostat in a room is where TRVs go. In particular, it's so close to the hot pipes feeding the radiator that it must be affected by the circulating water temperature. The temperature sensed by the TRV is a combination of the room temperature and the temperature of the water flowing through the radiator. So at first sight you'd think it couldn't work. It does work because it is affected to some degree by the room temperature. That will differ according to flow temperature, radiator size (if the TRV's on the return) etc. But once set for a given room, it will keep the room within an acceptable temperature range. Of course, you'll never find a TRV calibrated with room temperatures because that's not possible.
As you recognise, TRVs can't call for boiler heat, so if the only control were TRVs you'd have to run the boiler continually. That's the point of your hall thermostat. It's intended to switch the boiler on anf off according to the general need for heat: as the weather gets colder, the boiler is turned on more frequently and for longer. It is not there as you supposed to act as a thermostat to set the temperature of the rooms in the house directly. It can't possibly do that, as you know. It operates indirectly to set the general level, allowing the TRVs to control the temperature in individual rooms (more or less).
What you are proposing (I think) is to let the room stat call for boiler heat. The TRVs in each room will only allow their radiator to heat if the room is cool, so even though the boiler operates to heat the flow water to all the radiators, only the cool room will have its TRV open so only its radiator gets hot.
The problem is that the TRVs in the rooms that are up to temperature will not have hot water flowing through them. The TRVs will then falsely perceive a fall in room temperature and they will open. So the room will overheat.
I know this is a bit complicated, but I'm sure you'll understand. You must be a bit more clever than average to have thought out your control method even though it won't work.
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Agile
Gas/Heating Expert
Joined: 18 Dec 2007
Posts: 40
Location: London/Midlands
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| Posted: Mon Nov 17, 2008 1:37 am Post subject: |
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Mr Shark,
I dont see why you are unable to set the hall radiator valves to be open just a LITTLE so that the heat output creates the same temperature rise as the rest of the house.
The heat input setting is very critical and rotational changes of only 10° to the valve shaft will make a lot of difference to the output.
How can I persuade you to try it? You have nothing to lose!
There are radio sending TRVs available from germany called Rondostats but they are way over the top for what you need.
The most you need is to fit a new room stat in the lounge ( using an RF unit to avoid any new wiring ).
Tony
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Mon Nov 17, 2008 2:10 am Post subject: |
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Not quite true Stoday, although I have know idea how good they are, but they retail around £40 quid.
And I don't know if you can have several on the same system, I assume you can, for what its worth.
First spotted them in a recent trade mag.
http://heating.consumers.danfoss.com/PCMPDF/VD53P202_RA-Plus.pdf
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Landshark2007
Junior Member
Joined: 15 Nov 2008
Posts: 4
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| Posted: Mon Nov 17, 2008 11:17 am Post subject: |
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Once again, thanks for the replies.
Perhaps I need to explain a little more. Our home has all the doors to each room SHUT at all times. We have a toddler and I work from home.
The hallway is where the only electronic thermostat lives and the hallway radiator does not have a TRV fitted. The electronic thermostat is set to 20 degrees.
I am now sitting in my front room where it is so cold, I am having to wear jumpers just to work. The hallway is 21.5 degrees so the boiler will not fire. All my radiators in my lounge have TRVs fitted and these are stone cold - why - because the hallway is warmer than the rest of the wretched house. 
Now, if I set the thermostat to say 22 degrees, the boiler kicks in and then everything gets nice and warm, and warmer and warmer, but because the hallway stays at 21.5 degrees (radiator is off) the boiler never kicks out. Sure - I can adjust the radiators in each room to stay at a constant temperature, but I need the boiler to kick out when that happens and it simply won't UNLESS I leave every door open OR turn on the hallway radiator which then switches off the boiler too quickly as it gets to heat in next to no time.
This is a fundamentally bad design and one that is costing me in lost tempers and frayed nerves. The only way that heat circulates is if the boiler is running and the radiators are warm. If the only way that this is started is via a thermostat set in the hallway, then it can never work correctly in a house where each room is basically isolated.
I need to have something to make this work properly - oil is expensive enough without this fiasco costing me! |
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Agile
Gas/Heating Expert
Joined: 18 Dec 2007
Posts: 40
Location: London/Midlands
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| Posted: Mon Nov 17, 2008 12:19 pm Post subject: |
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| Landshark2007 wrote: |
I am now sitting in my front room where it is so cold, I am having to wear jumpers just to work. The hallway is 21.5 degrees so the boiler will not fire. All my radiators in my lounge have TRVs fitted and these are stone cold - why - because the hallway is warmer than the rest of the wretched house.
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Here in London its 8.0 ° outside and 22.0 ° inside.
Can you explain to us what is heating your hallway up to 21.5 ° with the hall rad off? With cold weather outside its not obvious to me!
Another question! Why not turn the stat up to 22 ° so it turns on the boiler and then let the TRVs control the lounge temperature?
I am asuming you dont have the problem of the man who walked up the stairs to his office on the tenth floor but took the lift down!
Tony
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Landshark2007
Junior Member
Joined: 15 Nov 2008
Posts: 4
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| Posted: Mon Nov 17, 2008 12:30 pm Post subject: |
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Thank you again.
The 'background ambient' is 21.5 degrees in the house. By this, I mean that with all doors closed, the hall, stairs and landing are the only 'open' spaces from which the electronic thermostat is getting its reading.
The only radiator in this space is the hallway one which is currently turned off (the hallway is approximately 12' long by 4' wide).
From this is the door to the lounge which is shut, the door to the kitchen which is shut and the door to the cloakroom which is also shut. There is no radiator on the upstairs landing. The roof is well insulated and the house is double-glazed throughout. All radiators have TRVs with the exception of the cloakroom, hallway and bathroom.
The current temperatures across the house are:
Lounge: 15
Office: 17
Kitchen: 22
Hallway: 21.5
Bedroom 1: 18
Bedroom 2: 14 (radiator off and door shut not used)
Bedroom 3: 19
Thermostat set to 20 degrees.
Any of this making sense? |
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Agile
Gas/Heating Expert
Joined: 18 Dec 2007
Posts: 40
Location: London/Midlands
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| Posted: Mon Nov 17, 2008 12:39 pm Post subject: |
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I can see the temperatures you quote, but I still dont know how your hall stays at 21.5 with the heating off when its presumably not much different from my 8.1 ° outside.
Nor have you explained why you dont want to turn the stat to 22 ° and let the TRVs control the other rooms in the house and particularly the lounge and office which are too cool whilst giving a VERY small amount of heat to the hall rad so that it will raise the temperature there just a VERY little to eventually turn off the stat.
But keeping the heating off must save a lot of gas so its good for the planet if you must live like that. But I do like my 22.1 ° here !
Tony |
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Mon Nov 17, 2008 1:16 pm Post subject: |
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I prefer 25c during the day and 28c when dormant.
Looking at the figures quoted, it says to me either the radiators are not sized correctly, they are not balanced, or the hall is oversided.
Last but not least, the insulation or orientation will also make a difference, but should have been allowed for in the calcs.
A few simple steps would be to throttle the hall radiator right down, so it heats slower than other areas, Balance the other radiators to put more heat where it's needed.
All the above is cost free, after that you can zone each room and control the temperature with local stats, you could move the room stat, maybe install an RF stat and receiver, then you could take the stat with you to whichever room required controlling.
Before I retired I could have installed a system for you which would set the rooms at +or- 1 deg of any temperature you wanted, and then linked it all up to a computer, so you could sit in the office and play. The downside is an average system we installed was nearing the £200k.
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Scruff |
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Agile
Gas/Heating Expert
Joined: 18 Dec 2007
Posts: 40
Location: London/Midlands
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| Posted: Mon Nov 17, 2008 2:12 pm Post subject: |
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| thescruff wrote: |
A few simple steps would be to throttle the hall radiator right down, so it heats slower than other areas, Balance the other radiators to put more heat where it's needed.
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A little used trick to deal with too great rad outputs affecting room stats like this is:-
Isolate and drain the rad and refill without bleeding ( on an unpressurised system )
This will only leave water circulating through the lower part thus greatly reducing the heat output which is controled further by the valves.
With a pressurised system this will not work so well as the system pressure compresses the air in the rad so its necessary to pump air to further depress the water level.
Tony |
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