I'm new to the group, but I have been searching through Google for my answers, but am a little confused.
We live in a 1920s solid brick semi, and have an Ariston Eurocombi boiler with rads in each room which has TRVs installed, except the bathroom which doesnt have a TRV. All the TRVs are open fully, and when we want the house hotter or cooler I turn the heating thermostat down on the boiler itself. Is this an efficient use of gas? If not, is there a more efficient way of setting the heating? Is it worth leaving the boiler temp alone and tweaking each TRV? I've also read about installing a thermostat somewhere in the house. How does this work with TRVs?
My aim is to use less gas whilst keeping the house at a comfortable temperature (which, of course, is what everyone wants from their heating!)
Sorry if this has been covered before, I'm a bit confused!
yes, that is the whole point, you adjust the trv to give the temp you want in each room.
Yes that is the normal thing, problem at the moment is that the boiler will 'cycle' (fire up, burn for a short time, turn off, do it again) when the trv's close down. by sensing when the house is up to temp (well the room it's in - but it's best placed so that it doesn't shut down too soon) it turns off the boiler/pump. There are alternatives such as flow sensors.
They need to be fitted to rooms without a trv. so as not to conflict.
I'd get a wireless room thermostat, connect it up to the system and then try it out around the house, I tend to prefer the hallway, others tend to prefer the sitting room, but where it works best is what matters.
Take the head off of the trv in the room you have it in. Once happy I's swop the trv with the manual valve in the bathroom if it will swop.
Ideally you should set the TRVs such that each room is at temperature that you want. The TRV should then maintain that temperature. Usually you would leave the temperature control on the boiler alone unless a particularly cold snap requires you turn it up{1].
You would normally not have a TRV in the same room as the main stat. This can be achieved in effect by simply taking the head off the valve thus leaving it "full on" all the time.
The room stat serves as a boiler interlock and will stop the boiler firing when the whole house is up to temperature. This will save you gas since it saves the boiler form firing when not needed.
[1] when deciding where to set this temperature it might be wise to do it in conjunction with balancing the radiators. I have not checked the stats on your boiler, but assume it is not a condensing boiler = hence you need to take care that the water return temperature to the boiler does not fall too low (under 54 degrees C) else you might start getting condensation occurring in the boiler. This is not good for them if they are not designed to cope with it.
The Ariston Eurocombi (at least models A/23MFFI and A/27MFFI for which I have the manual) has an integral automatic by-pass that allows you to put TRVs on all the rads.
Although while you can do this, it will defeat the ability of the boiler interlock (required by building regs) to work correctly.... unless you want to get complex with flow switches etc.
Actually it will stop the boiler firing when the spot where the room stat is located matches the temperature set on the stat.
If you (1) locate the stat in a cold part of the house it may never reach its set temperature although the rest of the house TRVs have reached temperature and are shutting down. In this case interlock is not achieved and the pump continues to run while the boiler cycles on and off.
Conversely, (2) siting it in a warm spot, it will reach its temperature way before the rest of the house and turn off the boiler whilst the other rooms are still cold.
The room stat needs to be sited in a spot where it is influenced by the house heating in an average way. This should not be very close to an outside door or window where it is always cool, or not close to a radiator so that the stat is activated as soon as that rad comes on.
The hall is often quoted as the best place, but that is far from always true. If the hallway is narrow and has a radiator it can heat up far too quickly (and cool too quickly if it has a draughty door) to be representative of the living quarters.
This is where the wireless (or RF) types are so valuable - you can try it in different places till you find the sweet spot.
I have just replaced a clunky old bi-metal stat in the hall with a wireless Honeywell CM67RF. The old stat was permanently wired right opposite the hall radiator (the only one without a TRV) in our narrow hallway, and it was useless. We had to keep re-adjusting it as the hall swung wildly in temperature, and it was serving as little more than a manual on/off switch. I have now found a position 6ft further away, in a sheltered position under the stairs, works well with the CM67 and the house is now *much* more comfortable.
The old stat turned the boiler on full blast until it reached its set temperature, and then turned off the firing. However, the heat continued to be emitted from the hot radiators and the temperature overshot.
The CM67 has intelligent proportional control and learns that the temperature can be maintained by firing the boiler for only, say, 5 minutes in every 20 minutes. This gives a very fine control because it tends to keep the radiators at a fairly steady 'warm' temperature rather than blasting them from cold to piping hot and back to cold again. Experience so far is that it does work very well.
Ed's point about fine-tuning the hall rad with a TRV has set me thinking. Now I have moved the stat away from that rad it might as well have a TRV put on it - once I have installed an automatic bypass. There seems to be a bit of a conflict though; the TRVs have to be set a little higher than the room stat or it will never shut off, even the CM67.
That's true, I should have mentioned that. If a flow switch is used, is there an off the shelf timer module to fire up the pump periodically to check if a TRV has opened? Or do we have to DIY that with a 555 timer?
Short-cycling, no. That's when the flow rate is too low and the boiler upper limit stat cuts off the flame whilst a room or tank stat is still demanding heat. While in burn-time modulation (i.e. proportional) mode the CM67 will not set a burn time less than a certain value (5 minutes I think but don't have the booklet handy now), and the user can choose from 3 or 4 preset minimum burn times.
I think you took my 'warm' too literally. I was trying to indicate that there is something more than simple on/off going on here. However, any on/off system is going to have the return water varying from cold to piping hot at some point so if it happens the boiler heat exchanger just has to cope. From what you are implying, I suppose the CM67 would get even more out of a condensing boiler.
Incidentally, there is a potentially confusing point to note on the CM67 display. Its LCD display shows a 'flame' symbol to indicate boiler demand, but this simply means the set temperature has not yet been reached. In other words this flame symbol stays lit even when the CM67 has the boiler in the off part of the on/off modulation cycle. The receiver box has green LED on it to indicate when the boiler relay is actually closed, and its then that the boiler should be firing.
If ordering one of these take care as there are a number of variants: Wired or RF, optimising or not, 7 day programmable or 5 + 2 day. All have 6 adjustable time/temperature points normally used to set 3 warm periods interspersed with 3 cooler periods, and these can be different each day (42 in all for the 7 day model!!). It does not switch off an night in the way a timer does - instead you just set a lower temperature at night (down to 5C - should be low enough!)
even after reading it I am not sure. You need a pair of volt free relay contacts which close when heat is required.
Why choose that obscure make instead of the 2 or 3 recommended on this group? Cost maybe? I admit the CM67RF Optimiser is expensive - I paid £95 for mine.
Don't you have a manual? Try asking Ariston to send you a set. I have 3, Technical Manual, Installers Manual, And Flue Options manual.
I have the manual but not the boiler here, so its rather difficult to see what the unclear instructions mean. If you have a manual it is section 2.11 on P14 of the Technical Instruction Manual. Sadly they have goofed the editing and half the text is missing (they printed the first half twice *!*!).
Essentially it says
1 take off 4 screws on bottom part of boiler
2 Splay sides apart so control panel can be rotated down
3 Open the cover on left side of the compartment
4 Clamp your wire (from the receiver box relay) under the cable clamp
remaining instructions are missing, but from the fuzzy photos it seems to be
5 Lift out a 2-way connector block from under the cover removed at 3. This has 2 wires going back into the boiler from one side of it, and a link on the other shorting those 2 wires together.
6 Remove the link
7 Connect the 2 wires from your relay box in place of the link. Cable for this should be 3 Amp minimum.
The boiler time switch will over-ride the remote stat, so probably best to set it always on.
It is cost to be honest....this model I've seen for £40. BUt I dont want to buy it and find its not compatible.
Sorry, meant to say, I do have the installer manual, and I can see where the
2 wires for the stat go into, its just that on the stat I was looking at, I wasnt sure which wire would go where. Would the CM67 work OK? Is it compatible with my boiler?
It is not clear from that grasslin pdf manual that the contacts are volt free, though they probably are. You'll have to ask them. What you need in any stat is a simple switch (a relay) that just connects the two wires together when heat is needed, otherwise leaves them open. It does not matter which way round the wires go. Have you looked at the stat Ed Sirett recommends from time to time? A Horstmans Centaur from Screwfix if I recall correctly (google for his post). If cash is the main driver, the wired version of CM67 is much cheaper, as not only does it not need the RF circuits, it does not need a separate thermostat and relay box because the relay is in the thermostat box.
Yes and yes. I have another one ready to install in that exact boiler for my daughter.
Great advice Phil, many thanks. It has to be wireless as the wife hates anything with wires! We have wireless internet, wireless alarms, wireless doorbell......
Think I'll go for this one then. Seems from reading this group that its a popular choice.
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