fitting a thermostat to control overall temp

hi everybody i've got a combi condensing glowworm boiler connected to a drayton timer, plus TRVs on all but the bathroom rad. the problem is i dont have enough control over the overall temperature, the only way i could use the TRVs to do this would be to leave the heating on all day, then when the flat was up to temp, all the rads would shut off. the problem is i guess this would cost a lot to have the boiler running even if no rad's require the hot water. the timer is just inside the kitchen wired up to the boiler, i want to get a thermostat and put it on the other side of the wall (just inside the lounge), so that i can set a minumum temperature which the boiler will come on if it gets too cold in the lounge. this is the programmer i have:

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this is the thermostat i think would do the job:
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this work? not sure what 3 wire means and if its compatible? hope somebody can help!

Reply to
benpost
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would this work? not sure what 3 wire means and if its compatible?

It would work, although it is not very sophisticated - basically allowing one preset temperature that will be obtained any time the timer permits the boiler to run.

You will need to defeat the TRV in the room with the stat - just take the head off it, and the valve will behave as if it is full on all the time, which is what you want to save the valve shutting off that rad before the main stat shuts off the heating, thus defeating its purpose.

The three wire bit means you need three wires (plus earth) to connect it up - live in, switched live out, and neutral.

If you went for something like:

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would let you have different temperatures at different times of the day. In fact a programmable stat makes the programmer redundant to all intents - you just leave that on continuous, and the stat then does what is required to have the temperature you want and when. So for example you can say keep the temp overnight no lower than 15, rise to 21 when I get up, fall back to 15 during the day, and get up to 20 when I get home etc. The one linked to is a 7 day one as well, so you can have different patterns on weekends etc.

The digital stats are usually battery operated (batteries in these cases literally last for years), and are typically two wire devices, i.e. they don't need the neutral connection.

Reply to
John Rumm

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> would this work? not sure what 3 wire means and if its compatible?

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> This would let you have different temperatures at different times of the

I have had one for several years _ it is absolutely the bees knees. I guess with hindsight one with a 'holiday' setting for the odd winter break would save a bit of reprogramming. If wiring is a concern then look at wireless ones. (and ditch the timer)

Reply to
John

that looks really good , i was thinking of trying something though before changing the system. i figure the plumber must have had his reasons for fitting a fairly expensive timer (drayton sp4?) along with TRVs, and it was also suggested by a family member. is it worth leaving the timer ON all the time, and using the TRVs to control temps? for example put them all on number 1 setting (or frost setting if on holiday) then only increase them if i'm using a room and want it warmer?

with the timer on all the time, how much wastage is there in terms of gas and electric if the boiler is only occasionly having to top up the water temperature?

also just because i'm a novice, with a combi condensing boiler and no water storage, how often does the system use mains water? does it recycle the same water at all? is water being pumped around the whole time the timer is on?

Reply to
benpost

Lack of awareness of prog stats possibly. You want the TRVs either way, but programmers on combi systems are of limited use.

Not really - the boiler will still run far more than it needs to.

The problem is if the boiler is on and in its heating mode (i.e. there is a permanent call for heat since there is no room stat) it will keep attempting to run. Once the rooms are warm enough, the TRVs will close off leaving only the bypass radiator to absorb the boilers output - which it won't do all by itself. Only when the return temperature rises to the point where the boiler can't heat the water any more will it stop on its own internal thermostat. Needless to say the boiler will cool, and then have another go, even if the house does not need it.

Only when you turn on a hot tap.

There is a closed loop full of water, this is called the "primary circuit". It passes through all the rads, and the main heat exchanger in boiler. The pump in the boiler circulates it when its running. It should stay there, and assuming no leaks are present in the heating system will rarely need topping up (there will be a filling loop, and pressure gauge somewhere to allow you to fill it, and see that there is enough in there)

When you turn on a hot tap, a flow switch in the boiler senses this and activates a diversion valve. This diverts the heated primary water from the boiler through a plate heat exchanger instead of the radiators. It then flows straight back to the boiler again (in effect turning off the heating while the tap is running). The cold mains water flows through the other side of the plate heat exchanger, is heated by the circulating primary water, and comes out hot.

The pump will often run all the time the call for heat signal is there from the thermostat. Hence you may find it is on all the time your programmer is on at the moment.

Reply to
John Rumm

That models is large a horrible and I would not have it in my living room. Some of these devices have remote room sensors which are nice and neat, so the control setting side is in a position that is unobtrusive.

Reply to
Doctor Drivel

Sorry, only English spoken here.

Reply to
Steve Firth

Oh look! A plantpot. This one needs tagging.

Reply to
Doctor Drivel

if i bought the all in one thermostat/timer in the link then i'mguessing the thermostat is built in, which means it would be in my kitchen, am i right saying a kitchen isnt the best place for a thermostat? i'm quite happy with the drayton timer i just want a thermostat wired up to it on the other side of the wall (one side lounge, one side kitchen).

Reply to
benpost

i doubt id be able to sell my drayton programmer so i was going to keep it and just connect up a thermostat in the lounge and wire that to the programmer. leaving the programmer set ON so the thermostatt will decide if the system is on or off. and leave all the TRVs on full so they wont shut off before the thermostats level. does this make sense and would it work ok?

Reply to
benpost

just to make it clear this is the programmer ive got

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i just want to be able to have the system come on based on an overall temperature. the last few days having the heating on the ON setting has been ok, but when it warms up slightly then i dont want it always on, and i cant set the timer to accomodate because you never know what the temp might be at any one time!

Reply to
benpost

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That's what thermostats are for... Personally I would leave the programmer wired in, and add a prog stat. Then just program the stat for what temperatures you want, leave the programmer set to "continuous" and forget about it.

Reply to
John Rumm

It all depends on how warm you want each room in the house to be, and at what times of day you need to heat them to a particular temperature.

Having one thermostat in one room to control the whole house, is not a very good plan of action, in my way of thinking.

If you could install a thermostat in each room, which is what the TRV's are for on radiators, and then combine them to find a mean temperature from throughout the house, then your idea may have a working prospect.

Having a central thermostat in the center of the house may give a mean temperature, but then you have to consider which doors are closed on which rooms, which are not then contributing to the central core mean temperature for the central thermostat to detect.

In my opinion, having an over temperature thermostat in the boiler is enough. Then leave the TRV's on each radiator to regulate the room comfort levels.

Balancing the system may have a better effect on your homes overall heating comfort.

Reply to
BigWallop

hi big wallop...

In my opinion, having an over temperature thermostat in the boiler is enough. Then leave the TRV's on each radiator to regulate the room comfort levels.

what is an 'over temperature thermostat'??

cheers

Reply to
benpost

It's a safety device that shuts the boiler off, if all the thermostats or controllers fail.

Reply to
BigWallop

This is specifically prohibited in the building regulations however, because there is no way of telling the boiler not to fire once the house is warm enough - it will keep cycling on and off as the water cools and gets re-heated.

Indeed this is worth doing. Having TRVs will also allow you to fine tune the temperature in each room, so also well worth having. A room or zone stat is the final bit in the picture that ensures the heating only runs when actually needed[1]. In its simplest form (i.e. one room stat for the whole installation) its not ideal, but in many cases works well enough if everything is setup carefully.

[1] In theory anyway - obviously its not perfect and hence will not always get the desired result - say when the stat is in the hall and the front door is left open for a long time etc.
Reply to
John Rumm

my friends dad is an electrician and was here yesterday i asked him about it and he said i could just add a thermostat and connect it to the existing timer/programmer and put it the other side of the wall in the lounge.

would one of these do the job? i notice one says combi stat?

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Reply to
benpost

Yes but they are single fixed temperature (unless you manually adjust it). These days I'd only think about fitting a programmable stat, these allow the set temperature of the room to be controlled on a time basis. Far more comfortable than the simple on/off single temp stats.

Screwfix only list two under "programmable room" but I don't think their descriptions are accurate on many of the other room stats they have available. They use an exprssion like "6 On/Off Periods per Day" which to me says the stat is on or off with a single set point not that it controls the set point temperature based on time of day.

Google to see what is out there.

Reply to
Dave Liquorice

Yes but they are single fixed temperature (unless you manually adjust it). These days I'd only think about fitting a programmable stat, these allow the set temperature of the room to be controlled on a time basis. Far more comfortable than the simple on/off single temp stats.

Screwfix only list two under "programmable room" but I don't think their descriptions are accurate on many of the other room stats they have available. They use an exprssion like "6 On/Off Periods per Day" which to me says the stat is on or off with a single set point not that it controls the set point temperature based on time of day.

Google to see what is out there.

Reply to
Dave Liquorice

If you have one thermostat to control the whole system, then it should actually be placed in the core of the house (like the hallway or the bottom of a staircase). Installing a 'stat in one room will only detect the heat level in that room. The rest of the house will not be the same temperature as the room the thermostat is in. You have different configurations of air movement around different parts of the property. Not all rooms may need to be heated in the same way as the living room because they have sunshine coming in through windows for most of the day and other room may have different insulative properties than all the other rooms around the house.

If you want to keep the whole house at the same temperature, you would really need to fit a thermostat in every room and combine their detected inputs and outputs to a central controller that only switches on or off if all the thermostats reach your set level.

But a simple room 'stat like this

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would do the job you want.

Reply to
BigWallop

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