Controlling heating with no thermostat

sxp842

Hi all

We have moved into a new property and replaced the boiler with a Viessman Vitodens 100w combi boiler. However, we don’t have a thermostat installed yet.

So far, we have been trying to control the heating directly from the boiler. We normally set the heating on the boiler control to about 50 during the day and 40 night, and the water on 60. We also have thermostatic valves on our radiators. However we have just got our first heating bill through and it’s much higher than we were expecting. 

Is there any way we can more efficiently control the heating via our boiler, if we don’t have a thermostat? In previous properties I’ve always controlled the heating via the thermostat and timer, rather than directly from the boiler, so I’m not sure if we are doing it right?

any advice would be appreciated.

our radiators are also set on max but are only warm rather than hot. I’m not sure if this is anything to do with the boiler problem?

southcoastrgi

No thermostat doesn't comply with building regs, it also doesn't comply with boiler plus, this could get both you & the installer a £5000 fine, why wasn't one installed at the same time as the boiler ?

Easiest way is to get a wireless boiler+ programmable room stat then you won't have the hassle of running wires.

Jeepers_Creepers

You have your boiler set to provide radiator water at 50oC and you find the rads are not that hot? Hmm, how could that possibly be...?

What I can pretty much bet is that your boiler runs continuously whenever it's timed to be on? Does it actually get your house up to a comfy temp?

Who fitted your boiler - was it 'official'? Because whoever did so wasn't bothered that your system didn't have an 'interlock' - a weird name for a device that turns your boiler off when demand has been met. Eg a room stat. I understand this is against regs - so who did install the boiler?

Since your boiler is running at a pitiful level, I'm surprised it's seemingly using more gas than the one in your old house.

You really should install a room stat, but meanwhile there is nothing basically wrong with having it running all the time and using TRVs to control the room temps. It's not very efficient, but since your boiler is running at only 50oC, I'm not sure that efficiency is an issue.

Is your house warm enough? If it is, then 50oC water flow is great as your boiler will be in full condensing mode, but I suspect that your house just ain't that warm?

southcoastrgi

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fenwick458

sxp842 said:

Is there any way we can more efficiently control the heating via our boiler

yes install a thermostat.

sxp842

Ah, we were going to install a nest thermostat but haven’t been able to do it yet because of our electrics. We should have that installed in the next few weeks. Although I never realised that the thermostat was part of building regs. It sounds like that should have been installed at the same time as the boiler. 

I don’t know if there is an interlock, is there for me to tell? The guy who installed it was gas safe registered (I think that’s what it’s called) but it sounds like he maybe didn’t do a great job.

sounds like I’ll need to get another gas man in to come and look at this.

also, is 50 low for the boiler? What sort of temperature should it be running at?

southcoastrgi

Time & temperature control is your interlock, it really depends how old your rads are & how well the heating calculations were done, modern rads are worked on a DT of 50 so should heat the room correctly at that temp, older rads have a DT of 70 so require that temperature, heating flow is on average set at 70° on the boiler, quite a few systems just relied on trv's on the rads to control temperatures but that doesn't comply because there is nothing to turn your boiler off so it just keeps turning on & off to maintain the temp you have it set to, if you are going to get a nest fitted in a couple of weeks then I'd wait until then but yes you are correct it should have been installed with the boiler, when he registered it with gas safe you will automatically get a building compliance cert sent through but by doing that he has lied because it doesn't comply 

fenwick458

I wouldn't get to concerned about interlocks or boiler temps, a simple programmable thermostat should sort it out.
any electrician can fit a thermostat to a boiler, its a simple job, doesn't need to be a gas engineer, ball park £100-150 depending on the stat fitted

Jeepers_Creepers

Sxp, I don't think you should get hung up on your gas bill. You will simply need to pay for whatever you need to use to get your home to the level of comfort you require.

Your new boiler looks like a very neat machine - SS exchanger (good), very high efficiency rating (good). I think you can safely assume that no other boiler will do the job better or more efficiently. So that's all good.

Your rads are not hot, tho'. That is because you have the boiler temp set too low - 50oC is nothing, certainly not during winter. What will be happening at the moment is, your rads will likely not get your house up to a cosy temp (I can't see how they can at 50oC) so your boiler will simply be running constantly, obediently churning out 50oC water for as long as it's turned on.

50oC might be fine for milder temps - you might be able to turn it back down there come Feb, for example - but when it's 3-5oC outside the chances are you need your boiler to be putting out at 70oC, possibly even more. You then set each TRV to suit the room they're in; 3to4 for living areas, 2to3 for bedrooms (and down to 1 during the day) etc. A miracle will now occur - the rads will get HOT in the mornings when you turn on the boiler, and your rooms will - gasp - become warm and comfy before too long. Then - ooooooh - the TRVs will shut each rad slowly down/off as the room reaches the set temp. Jobbie jobbed. You want your room cooler? Tweak the TRV down a half-number. Warmer? Open it ditto.

Except your stupid boiler will keep trying to run because no-one fitted an interlock.

In practice that ain't a major problem, as it'll shut the burner down when it cannot shift the 70oC water.

It's worth having a look at your boiler to see if it has 'Opentherm'. If it does, then it might be worth getting controls that'll take advantage of this - I think Nest does? What this will do is not just turn the boiler on and off like a normal room stat, but tell the boiler to 'modulate' up and down so that it keeps the water temp at just what's needed. I think.

Also consider 'weather compensation' if it can have this feature. The cooler you can run your boiler, the better - the more efficiently it'll run as it'll condense more of the flue exhaust and extract energy from it. 50oC is great for that, but unfortunately not hot enough for your rads in winter. What W-C will do is to sense the outside temp and then tell your boiler to produce the coolest water it can that'll still get your house warm. So it'll likely make it ~70oC when freezing outside (or even higher), and automatically reduce this as it becomes milder.

If you were fitting a completely new radiator system now, then you'd 'oversize' the rads compared to the ones you currently have. The idea is that a larger rad will give the same overall output to the room when running at 50oC that a smaller rad will at 60oC (ballpark figures, of course). So you can always run your boiler at a low temp = more efficient.

What you need to do, tho', is run your rads at a temp that gives you what you need in your house. If your house is fine with rads running at 50oC, then great. But I bet it ain't... :-)  

Robin9

sxp842 said:

................................ However we have just got our first heating bill through and it’s much higher than we were expecting. .................

Just checking - is your gas bill based on ACTUAL readings or ESTIMATED  ?    Keep putting the meter readings in - perhaps always on the last day of the month ie today)

and what's much higher than expected - January is a winter month.