Combi regulations

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Alfies Revenge said:
Is it now a reg to fit a room stat with combi boilers

kind of always has been but tightened up like BOB says wif part l1
 
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Alfies Revenge said:
Is it now a reg to fit a room stat with combi boilers

No.

Part L says, you must fit a boiler interlock, a room stat is one type of boiler interlock.

(some combis have built in flow switches and if fitted to a full TRV system they do not need a room stat).
 
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Electrical isolation of the boiler so it cannot fire up unless either the rads are calling for heat or a tap is turned on.
 
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I thought trvs wernt technically a boiler interlock as they don't tell the boiler to go back off, they just block the flow of water.The boiler will still try fire till the temp in the pipes are too hot.
 
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This is some half a7sed Baxi setup being referred to. Not that I have spent my time worrying about it, but I can't think how relying on a boiler flow swtich to act as an interlock for the heating could do its job properly.

What happens when the boiler shuts down, the trvs open and there's no stat installed to call for more heat? With the boiler shut down there is no flow to kick it back on - unless the pump is spinning wildly against a closed circuit.

Perhaps I missing something. But the boilers are w@nk so it is not high on my list of worries.
 
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Dan Robinson wrote

What happens when the boiler shuts down, the trvs open and there's no stat installed to call for more heat? With the boiler shut down there is no flow to kick it back on - unless the pump is spinning wildly against a closed circuit.

I think their is a control circuit which pulses the pump on/off periodically to check for flow though I stand to be corrected on that.
Standard wall stats are not very accurate anyway and I am sure a lot of people just turn them up high anyway.
With the flow switch each individual TRV will have control over the boiler interlock and has the added advantage of proportional temperature control over each individual room space temp and not just an on/off as dictated by an inaccurate room stat in some dodgy location adjusted to an even more dodgy setting by the user.
IMO. :)
 
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I agree the old style stats were a bit hit and miss (although Honeywell claim 1 degree accuracy :confused: ); but the new ones are very accurate. My CMZone and CM67 stats are within half a degree and have been for over 2 years.

If your description is of how they work then it makes sense - kind of. You have to admit though, it is a sh1t idea. Especially when you consider how unreliable trvs are - and some don't actually turn off completely either.
 
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Dan Robinson wrote

My CMZone and CM67 stats are within half a degree and have been for over 2 years.

Above average control system, though I dont like the idea of running around replacing batteries in those every so often :( .

You have to admit though, it is a s**t idea

Not at all. Its not convention and probably not understood, thats all.
You may as well say your CM zone system is a sh@it idea.
How many people would have the slightest clue how to use CM zone. ?


Especially when you consider how unreliable trvs are -
and some don't actually turn off completely either.

Quality ones are not unreliable. Danfoss's RAS-C and RAS-D range have positive off sensors so no flow gets through.

If flow is a problem then flow switches which can be individually set to operate at a flow rate matching the application could be used.
 
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Balenza said:
Dan Robinson wrote

What happens when the boiler shuts down, the trvs open and there's no stat installed to call for more heat? With the boiler shut down there is no flow to kick it back on - unless the pump is spinning wildly against a closed circuit.

I think their is a control circuit which pulses the pump on/off periodically to check for flow though I stand to be corrected on that.
Standard wall stats are not very accurate anyway and I am sure a lot of people just turn them up high anyway.
With the flow switch each individual TRV will have control over the boiler interlock and has the added advantage of proportional temperature control over each individual room space temp and not just an on/off as dictated by an inaccurate room stat in some dodgy location adjusted to an even more dodgy setting by the user.
IMO. :)

Some smart pumps slowly turn when all TRVs are closed. The Baxi has the added advantage in that is will ensure minimum flow through the heat exchanger.

You can rig your own flow switch and pulse timer to provide an interlock using TVRs all around. The problem is getting the minimum flow through the heat X before the flow switch switches out the burner. It is possible having a by-pass around the flowswitch with an in-line adjuster in it. To set up you need an expensive flow meter in the line which is then taken out after setup.

Another way is have a small buffer in the CH circuit - could be a 40 litre cylinder or preferably sized to the same water volume in the rads and CH pipes. The boiler heats this with full flow always with a fixed rate pump. A stat on the cylinder cuts out the boiler (best use two to prevent boiler cycling increasing boiler life and reducing breakdowns; a cheaper, non-modulating, simpler boiler can be used). The CH circuit is taken off the cylinder and a smart pump used (like a Grundfos Alpha or Wilo Smart) and TRVs on all rads. The buffer could be preheated to supply instant heat to rads in the morning.
 
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Balenza said:
If flow is a problem then flow switches which can be individually set to operate at a flow rate matching the application could be used.

These are difficult to source and not cheap tending to be commercial products.
 
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Dan_Robinson said:
I'm still not being convicned that it is a good idea...

A flow switch as a boiler interlock? A think it a very good idea if done properly. It adds to efficiency as no auto by-pass valve is needed which raises the return temperature.
 
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