My neighbour has just had a new Baxi combi installed. They've put TRVs on all the rads bar one and have ripped out the old room thermostat. Is this normal? I find being able to set that to 15 or so useful if you're leaving the house unoccupied for a few days but maybe that's not how it's done these days. The rad without the TRV (in the bathroom) you could fry an egg on. Just as well there aren't any kids about. It looks as though you can adjust the CH temperature on the boiler but it's already below 50% on the scale.
In article , stuart noble on all the rads bar one and have ripped out the old room thermostat. Is
Normal for a poorly designed installation, yes. And remember that heating system electrics are beyond most plumbers.
Most sensible installers would recommend a programmable thermostat which allows different temperatures to be set automatically throughout the day and days of the week. You can set them for different temperatures for night, morning, when you're out at work, and evening. And have designated 'weekend' days where you're likely to be in and want the same temperature all day.
So if the weather gets very cold you alter the thermostat on the boiler? Very convenient, that. For the installer's profits, certainly.
You switfh the whole heating off really. Or turn the TRV's down to frost settings.
ou need one rad that doesn;t shut down, or some other form of bypass - a radioator that will take the full flow when all teh others are shut down.
Bathroom is good since its a small room and needs the heat to keep condesation down. Another option I favoured in the past was a small rad in an airing cupboard. You can also fit a bypass loop that allopws teh pump to circulate hot water without doing very much heating at all.
There must be some sort of boiler interlock installed. Otherwise, the system does not comply with the building regulations. The interlock is normally of the form of a room thermostat. However, it is permissible to use TRVs and a flow switch to detect that all the TRVs have closed off. You need to find out if your system has such a switch. If it does not, get the installer back and ask how the boiler interlock requirement of Part L1 is met.
Actually, thinking about it, it can't be compliant, as the bathroom radiator without the TRV would mean that any such flow switch would be ineffective.
"stuart noble" all the rads bar one and have ripped out the old room thermostat. Is this
Lunacy. Who wants to go round the house 2 or 3 times a day turning rad stats up and down? I'd get the fitter to put in a programmable room stat and save all the hassle (and a load of money on unnecessary heating).
Ours had been installed like that. I bought a Danfoss TP5
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is terrific. It beats going round 17 rads when I want to just tweak the temperature a bit. I like being able to set an 'overnight' temperature
- somewhere between a froststat protection setting and the usual evening setting. So if it gets really cold overnight, the heating will come on, just enough to take the bite out the air.
True, but they'd have to be brain dead to get rid of the room stat, it's only 2 wires. At worst they could have just used an old fashioned one and turned the temp up and down as needed, still easier than going round all the rads.
It sounds more like a rip off than incompetence, I wonder how much each of those rad stats were charged at?
My Part L building regulations have no mention of use of thermostats beyond stating thet either TRV's or other thermostats should be used.
Ther is no issue with teh boiler running continuously. Boilers stop when their own internal stats detect the return flow is up to temperature.
I seen no reaosn to install flow switches unless too simply protect the pump...but a bypass loop does that anyway. Also how does the system detect the condition when a TRV has opened up? It can't unless teh pump is switched on to check flow rate...
There seems to be an urban myth here.
With a TRV system, the idea is to pump more or less continuously, and let the TRV's decide on demand. The boiler merely cuts in when the return flow has dropped to the boiler stat level.
Use of TRV's with an overall zone stat makes them essentially useless. Either they are still demanding heat when the main stat cuts out, or they have shutdown before it itself does, in which case it never does.... you cannot have a romm or area controlled by two stats on essentally the same zone.
With all due respect, you and Christian are talking what appears to be twaddle.
How about page 16, paragraph 1.41 "b) Where it is proposed to effect control by thermostatic radiator valves, a room thermostat (or other device such as a flow switch) should also be provided to switch off the boiler when there is no demand for heating or hot water."
Also page 19 "d) Boiler and hot water storage controls. So that replacement boilers (other than solid fuel boilers) and hot water vessels can achieve reasonable seasonal efficiency, the work may also need to include replacement of the time switch or programmer, room thermostat, and hot water vessel thermostat, and provision of a boiler interlock and fully pumped circulation. Section 3 of GPG 302 34 gives more advice on how this can be done."
FWIW I have a full TRV system (i.e. no rads without TRVs), with an auto-bypass loop at the boiler, *and* a programmable room stat in the hall.
The TRVs are set so that, in the evening, the rooms are each at the desired comfort level - thereby fulfilling the aims of a full-TRV system as you describe it.
However, the hall-stat is set (at 21C in the evening) to shut down the boiler when all rooms are up to temperature.
In the morning we have the hall stat set to 19C, as we're rushing around and don't like it too warm in the mornings. There's no way we could do this without that stat in the hall, unless we went around and altered the TRVs all the time.
We do get in the situation where some rooms are not up to temperature and the hall stat shuts the boiler down - this is as you predict, so against all advice I have fitted a TRV on the radiator in the hall too. This I set a little cooler than we'd ideally like, so the hall is the last to warm up - it needs heat "leaking" from other rooms to finally hit 21.
It's a bit of a fudge, but I can't find a better way of doing it! I suppose you might argue that that we might as well set the stat to 45C in the evenings and let the TRVs do their job, which is fair enough, but we still need the stat to achieve a lower temperature than the TRVs would allow.
So, with all due respect you are talking what appears to be twaddle :-) Well, partial twaddle maybe.
The requirement is new from the 2002 building regulations. I suspect you are simply still thinking in terms of pre-2002 requirements.
No, the thermostatic switch is not enough. It must totally turn off and not keep the primary circulating water hot. As every single gas/oil boiler in existence has such a thermostatic device (or similar analogue modulating control), why do you think they would mention room thermostats or flow switches as interlock devices?
If the system you propose is installed, the boiler will operate (to heat primary circulating water) even when all TRVs are closed and the hot water cylinder is hot. This is not allowed. I'm afraid you appear to be in a minority of one in insisting that an all TRV system is allowed without room thermostat or flow switch.
Indeed. There are three methods proposed.
a) Install TRVs and a roomstat. You can balance and design the system such that the TRV rooms heat up marginally quicker than the room thermostat rooms. This ensures that the TRVs turn off before the room thermostat engages the boiler interlock. This provides good temperature control in all rooms.
b) Install a flow switch that determines that when no flow occurs through the TRVs, the boiler is turned off, and the circulating water cools down. This provides even better temperature control in all rooms.
c) Install a fully controlled zoned system (i.e. room thermostat/no TRV in every room).
Set the TRV to full (preferably replace, so the radiator is lockshield both ends). Then balance down the hall radiator using the lockshield so that it warms up slowly and doesn't get very hot. Then, when the other radiators get shut down via their TRVs, more water gets to the hall radiator. By the time all TRVs have shut, the hall radiator gets the full force of the boiler, heats the hall and the room stat shuts down.
This would defeat the boiler interlock and make your system inefficient, as the boiler will continue to short cycle, heating your primary water which may lose heat into areas not required to be heated.
That would work, but the advantage of my approach is that the hall rapidly gets close to temperature, then takes a long(er) while to get to final temperature. This has the effect of making it seem to warm quickly.
Your approach would result in the hall seeming colder for longer, but would work.
It refers to it as a control interlock. Can be a flow switch. In short, a device to switch out the burner when the house is up to temp. A boiler is not allowed to cycle unnecessarily.
That is cycling - NOT ALLOWED.
That is because you don't understand.
Not so.
Good idea.
What if all rads have TRVs? Then the boiler cycles. So a flow switch is necessary to cut out thre burner.
Not useless, just less effective. If the room stat is in the coolest part of the house, usually the hall, and the rad is sized and balanced to give the desired room temp, then if this room is satisfied then all the others are. As it is the coolest room in the house it will demand heat before the others, so the other room will not be cool.
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