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Potential systems without a room stat

View the thread, titled "Potential systems without a room stat" which is posted in UK Plumbers Forums on UK Plumbers Forums.

awkwardcustomer

awkwardcustomer

I would love some phrases or sentences from an expert to describe central heating boiler configurations with just feedback from TRVs (no room stat in the design).

If there are some configurations, manufacturers or combinations which work better for TRV-only it would be great to hear those ideas too.

I want to brief some UK, Europe installers who are coming to survey and quote for a new boiler. I just don't know the right words or reference hardware to mention so I don't end up with a conventional system and yet another bloomin' room stat.

BACKGROUND

I'm fed up with dealing with a room stat as an interlock to turn off the boiler. I've given up trying to explain to the family how the thing works and the song-and-dance of finding the wireless stat, checking its battery, checking it's in range, moving it into the right room, moving it back when the room isn't occupied or the TRV is turned down, with the feedback loop (or the missing feedback loop) routinely turning the house into an oven or an ice-box.

It's tempting to fall back on setting it to max and pinning it in the hall making it effectively always on, but given the existence of a bypass radiator which kicks out so much heat, this is simply a waste, and it doesn't even work properly as it'll take a while before a newly-opened TRV ever gets heat if the room-stat in the hall is already baking.

I am completely replacing my boiler now as the previous one got rain-damaged from a faulty flue installation. Now is my chance to ask the installer for a modern system which can use feedback from a fully-TRV system. Then to make a room hot, you just open the TRV, and people can expect the radiator to heat that room to that temperature fairly quickly.

The problem is that I don't know the right words for systems which operate this way. I've heard of some all-in-one systems which are designed to work this way. Welcome everyone's thoughts.
 
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Problem is it’s very inefficient as it will be on all the time when you set the program on the timer

Your better off binning the trvs and just going for lockshield valves and designing the system to run at 30-35 dc which will mean upgrading your rads
 
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Thanks for your help, Shaun.

The systems I'm aiming for would shut down the pump and the boiler when the TRVs aren't flowing, which I thought would ensure efficiency. Then it would only reactivate when flow is detected through one of the TRVs opening. Or are you already anticipating this kind of system and saying that it's inefficient? Where does the inefficiency come from?

I'm not sure I understand "going for lockshield valves and designing the system to run at 30-35 dc". I tried to search for 30-35 dc on google but I couldn't get a match.
 
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Here's some of the references I dug up about it, but still pretty vague on the proper wording I need to dig out from these specs, and whether there are different variations on how to deploy without a room stat...

Conservation of fuel & power in Approved Document L1 Design & Construction on page 16 paragraph 1.41 (b) 'Boiler control interlocks' indicates that a flow switch is enough interlock for regs.

"The Baxi HE Plus boi[l]ers and the Potterton Promax has integral flow switches so that TRVs can be fitted on all rads. When TRVs are all closed the boiler switches off via the flowswitch. The boiler periodically tests the to see if the TRVs have opened up."
forums.moneysavingexpert.com

High gas bills - possible meter issue? - Page 4

This is exactly the system we have which does not require a redundant room thermostat.
forums.moneysavingexpert.com forums.moneysavingexpert.com

"The interlock for the CH circuit can be provided by
either a Room Thermostat or a fully TRV’d system with
the pump wired back to the boiler without a bypass.
Connection diagrams for both options for Y and S plan
systems are shown"

"This boiler does not require a bypass.
This boiler does not require a permanent live.
These diagrams only refer to pump protection for fully TRV’d systems"
 
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I'm not sure I understand "going for lockshield valves and designing the system to run at 30-35 dc". I tried to search for 30-35 dc on google but I couldn't get a match.
Click to expand...

OK thinking about your reply I think you mean given the inefficiency I may as well leave all the radiators in free-flow on all the time at 30-35 degrees Centigrade is that right?
 
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Flow switch is for safety eg no flow of water eg no water in the system the boiler won’t fire it’s not for when the trvs shut

And it’s well know for the baxi ones to fail and melt the heat exchanger
 
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What's the occupancy of the dwelling going to be? Are you at work all day and just want one or two rooms warm when home? Or are you at home all day?
Click to expand...

It has varied wildly. A lot of the week it's just me occupying one room all day, (work from home in one of the bedrooms), but when my 9 year old is staying (half the time) she's all over depending where she's playing, or doing homework or project work in the workshop. It's nice to be able to choose which rooms we are using. Probably 50% of the rooms are unused any one particular day. Not long ago we had all 4 bedrooms occupied, with a Russian visitor and her son who were always battling with the heating when they arrived home and I wasn't in. Ending up baking some part while another was tepid or frozen. I tried my best to explain how the 'turner-offer' worked and how you had to be sure it was in the right place both to keep the heating on, but also to make sure it didn't overrun. Not much luck. It's destined to fail and pretty complicated to think about. People just want to be able to say 'this room should be normal please' without playing chess with the room stat. I'd love to be able to tell people - just put the Radiator to 2 and it'll heat up in 10 minutes. It's an old victorian house so the rooms in the roof take a lot more than others given their level of insulation. I'm working on fixing that.
 
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And it’s well know for the baxi ones to fail and melt the heat exchanger
Click to expand...

Thanks, Shaun. That's just the kind of thing it's worth knowing - if the systems that CLAIM to be able to do this are just plain dangerous maybe I should opt back into the room stat systems. I'd love not to have to deal with another two decades of room stat shenanigans if there are legit systems which do this properly. I'm not just after the cheapest there is, so if there's a more mature system that can do this properly I'd be willing to invest.
 
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If you were home all day and most rooms were occupied/needed to be at a constant comfortable temperature then I would suggest something like a Viessmann 200 with weather comp. Based on your sporadic occupancy though I would suggest something like Evohome as Shaun mentions above.
 
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The evohome sounds like the most practical way forward, which is a bit of a shame given the maintenance overhead and landfill of batteries in all the TRVs being replaced every 18 months but it's maybe as good as you're gonna get.

I looked into lockshield valves and rebalancing thanks, Shaun. Even with TRVs in the system might dialling in each radiator using the lockshield contribute something? I.e. if I can maximise the flow through the rads in the colder rooms in the roof, compared to the others it might mean the heating/cooling cycle isn't so asymmetrical - e.g. some central rooms getting hot and staying hot while the cooler rooms have long frozen. I guess it'll inevitably mean the hotter rooms take longer if I've throttled the flow, though.

What a shame there isn't a reliable system that uses feedback directly from mechanical TRVs as it would be so much simpler! It does leave you vulnerable to a failing TRV, but the worst that could happen is that you find it's too hot and get it serviced.
 
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Maybe the time to up size a few rads in those colder rooms then as advised above look at the viessman 200 boilers with weather compensation built in, you can control your boiler through a app on your mobile device It can be used without a room stat if you wish 😉. Kop
 
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In the end I have been quoted for either a Veissmann 100-w Combi 30kW (with built-in magnetic filter) or an ATAG IC Economisor 27 (with a filter as an extra) both would be fitted with an outside weather sensor as interlock, and neither would be fitted with a Room stat. They are both around £2900 to fit. They are also advising a power flush before the new fit (the previous was a failed Ideal Logic Combi 30) for an extra £350. Any reason to choose between these two?
 
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