Underfloor Heating controls

[Parmaslam]

Hi Everyone

I would like some advice on updating my electric underfloor heating controls, please.

My heating system was installed when the flat was built (c. 1970). It consists of electric elements embedded in the concrete floors. There are four zones - each is controlled by a simple 'Satchwell' bimetal strip thermostat.

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• Parmaslam
• 2 May 2014
• 1

The electricity for the heating is metered separately from the rest of the flat. It was controlled by a timeclock in the meter cupboard.

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• Parmaslam
• 2 May 2014
• 1

The timeclock died a few years ago (it stopped during an 'off' period). I told my supplier and a man came and moved it onto an 'on' period - so now I have 24hr cheap electric for heating

I'd like to replace the 'Satchwell' 'stats, charming as they are, with modern programmable thermostats. I want to have a warm flat when I get up in the morning and when I get home in the evening, so I want thermostats with that fancy 'optimum start' function where they 'sense' when they need to turn on to hit the right temperature at the right time.

So I have two questions:

1) How likely is it that my supplier will restore some kind of timer on my heating supply? (Because I'm not sure whether to get battery-powered thermostats or mains-powered ones).

2) Could anyone recommend some suitable thermostats that are capable of switching the currents involved? I've had look at the websites of some of the big names (Honeywell, Drayton) but they never seem to make it clear which 'stats are suitable for my 'old' system (and they introduce complicating factors such as floor sensors, which I don't think I need). I've measured the amount of current drawn by each zone as follows:

Living Room: 12A
Bedroom: 8A
Hall/Bathroom: 3.7A
Kitchen: 2.1A

Thanks for your help.

 

[Taylortwocities]

Syxthsense do a range of programmable stats. They all seem to have 16A rated contacts, which could stui your purpose.

http://www.syxthsense.com/thermostats/designer-range-of-networking-room-thermostats/

Have a look at the other stats in the range too.

 

[paul1949]

Hi
Did you find out what thermostat replaces the old Satchwell thermostat shown in photo I have the same type stat but have no details of it needs replacing
Many Thanks
Paul

 

[Taylortwocities]

If you want a Satchwell/Sunvic then you could use this one
http://www.tlc-direct.co.uk/Products/SATLM2253.html?source=shopping.com

Or use the Syxthsense TAM011

http://www.syxthsense.com/product/product_pdf/TH6.01-TAM-01.pdf

 

[JohnD]

now I have 24hr cheap electric for heating

most unlikely.

The meter facing us appears to have only one register, most likely peak-rate. But what is that glossy black thing to the RHS of your meter box photo?

Looking at your electricity bill, are you on a single-price tariff, or on something like an economy 7 rate?

The cost of electric heating is much higher than gas, but your old system relies on the concrete slab absorbing heat and releasing it slowly through the day. If you supply it at cheap rates it is not too bad. However the floor slab at that age will not be insulated to modern standards so you are also warming the worms.

 

[Parmaslam]

Did you find out what thermostat replaces the old Satchwell thermostat shown in photo I have the same type stat but have no details of it needs replacing

Hi Paul

I eventually went with the Drayton Digistat +3 (battery version - model 22083) http://www.draytoncontrols.co.uk/Digistat3ProgrammableRoomThermostats.aspx, mainly because I dropped on a couple of second-hand ones that were a good price (I didn't actually make a decision to go for a battery-powered 'stat, I just saw these and thought that they were a bargain).

They have yet to be fitted.

They appear to be adequately rated to handle the switching required for any of my heating zones

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• Parmaslam
• 23 Nov 2014
• 1

but I was concerned by the last sentence of step 3. in the installation instructions:

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• Parmaslam
• 23 Nov 2014
• 1

So I emailed Drayton with this query: "This thermostat is capable of switching mains voltage at currents up to 16A - why, then, do the installation instructions say that the battery version shouldn't be used for electrical heat applications?" They were very helpful - they explained that because of the relay type used in these thermostats, if the batteries failed while the heating was 'on', the heating would stay on continuously thereafter. Presumably this is because these 'stats use some kind of latching relay. I could see that this might be a fire risk for wooden floors, but as mine are concrete, I thought the risk for me would be very small.

So that's what I chose, but I wanted a programmable thermostat with all the 'intelligent' delayed start business. If you just want a straightforward direct replacement for your Satchwell thermostat, then the type that Taylor recommends is the sort you need.

All the best.

Parms

 

[Parmaslam]

The meter facing us appears to have only one register, most likely peak-rate.

This meter is controlled by the timeclock next to it. It supplies my underfloor heating only - on a restricted hours tariff.

But what is that glossy black thing to the RHS of your meter box photo?

That is the radio teleswitch, I believe. It controls the meter below it (two register) and switches between 'normal' (day) and 'low' (night) rates. This meter supplies everything except the underfloor heating in my flat.

Looking at your electricity bill, are you on a single-price tariff, or on something like an economy 7 rate?

My bill takes into account all three registers and I am on some sort of Economy 7 tariff (though it's called something else). At least I think I am - the last communication I had from my supplier stated that they were having 'an issue' around producing an account statement for me. We will see what happens.....

...your old system relies on the concrete slab absorbing heat and releasing it slowly through the day. If you supply it at cheap rates it is not too bad. However the floor slab at that age will not be insulated to modern standards...

I revealed part of the heating element while doing some work on my floor. It appeared to be laid on top of a layer of expanded polystyrene beneath an inch or so of concrete screed. That doesn't seem as deep as it should be, to me. I think that it should be deeper to get more of a slow-release effect, though it could've been shallow since it was at the edge of the floor.

As I have a cheap(er) rate supply for my heating, and I'm going to be installing my super new programmable thermostats, I'm hoping that my system is going to be as cost-effective as it can be. I don't have much alternative, as I don't have mains gas. (I often wonder, did they deliberately build flats without gas supplies in response to the Ronan Point explosion? (https://en.wikipedia.org/wiki/Ronan_Point))

...so you are also warming the worms.

At three floors up, I hope not!

 

[Taylortwocities]

Please remember that if you are on Economy 7 you will only be getting power to enable the heating at night time.
I am wondering why you need to have stats with complicated switching capabilities such as the Digistat? They won't enable/disable the heating at all during the daytime period.

 

[JohnW2]

Please remember that if you are on Economy 7 you will only be getting power to enable the heating at night time.

In relation to the meter+timeswitch which serves UFH only ...

The timeclock died a few years ago (it stopped during an 'off' period). I told my supplier and a man came and moved it onto an 'on' period - so now I have 24hr cheap electric for heating

I admit that it's all a bit confusing, since we are told that there is apparently also an additional 2-tariff meter (supplying 'everything other than UFH') controlled by a radio teleswitch.

Kind Regards, John

 

[OwainDIYer]

[(I often wonder, did they deliberately build flats without gas supplies in response to the Ronan Point explosion?

Although Ronan Point may have influenced things, other considerations would be nuclear electricity was going to be 'too cheap to meter' together with no maintenance costs for the landlord (I assume yours is an ex-local authority block; my flat was built with the same system but changed to storage heaters probably in the late 70s or early 80s).