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Topic Title: conventional boiler and cylinder
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Created On: 20 July 2013 10:27 PM
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 20 July 2013 10:27 PM
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SKElectrical

Posts: 910
Joined: 01 February 2009

Friend has asked for a price...
He installing a conventional boiler with a cylinder adjacent to it. He cant be bothered with the wiring.
Anyway he wants me to install a wireless room stat and a separate HW stat by the cylinder.

He is installing a 3 port valve ... AND then a 2 port before the cylinder. He says it's a failsafe - but my question is: is this the norm?

I've only ever installed 2 x 2 ports as a setup.
 20 July 2013 10:44 PM
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leckie

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So he's installing a standard y plan system with a second 2 port valve inbetween the y plan and the indirect coil into the the cylinder?

If so, what is he fail safeing against? Overheating of the cylinder? That's what the expansion pipe is for.
 20 July 2013 11:02 PM
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SKElectrical

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Originally posted by: leckie

So he's installing a standard y plan system with a second 2 port valve inbetween the y plan and the indirect coil into the the cylinder?
That seems to be it.


If so, what is he fail safeing against? Overheating of the cylinder? That's what the expansion pipe is for.

or a blow off valve if its unvented?


I don't know why he's chosen this.
It sounds simple enough.
 20 July 2013 11:43 PM
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peteTLM

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usually when a 3 port goes wrong, it parks in the middle so both heating and hot water get a share. They are not a 'hard' on and off like a 2 port, more of a rudder and a bit of persuation.

Ive never heard of this set up you describe. 2 ports go wrong 100% more often than 3 ports, and unless you have 2 cylinder stats to create a tiered effect, it wouldnt work anyway.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 21 July 2013 07:29 AM
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alanblaby

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Hmm, sounds a bit like the 2 plumbers who asked me to install the wiring for 2 underfloor heating zones on Friday.
UFH off existing CH system via 3 port valve. They have 2 remote thermostats for the 2 zones (house extension is just about finished - tiles down etc).
So I start with the 3 port valve, get that in to the expensive wiring centre, then the stats, then ask where the zone valve(s) were, to get them connected.
"What zones valves?"
Further questioning found the UFH was one big coil, not separated at all, so it was only actually one zone.
I tried to explain to them how wrong they were, but they insisted that the 2 stats made it a 2 zone system. Well, yes, it does, on the surface, but in reality, when one side is calling for heat, both sides are on, so no control at all, unless you wanted both rooms at the same temperature.
They really thought that the 2 stats would regulate the temperature individually.
I was quite surprised at how someone who fits boilers for a living, missed such a fundamental part of the installation.

So, to the OP, there is no need, (unless a custom, strange requirement) for a 2 and 3 port valve to be installed together on a conventional system. An S plan - 2 x 2 port valves is the most effiecient for the majority of installs. A Y plan can be a little easier for the plumber to fit in.
 21 July 2013 09:43 AM
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sparkingchip

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I tried explaining to a couple of plumbers why one UFH zone has to have two circuits of heating pipework one feeding in from either side of the zone so you end up with a even heat across the floor and the room, they totally ignored me and put one loop of pipe in!

If the system has a unvented hot water cylinder and it is y-plan then a two port valve and two cylinder thermostats are required for safety. However if the boiler has volt free controls it can't open a two port valve and you have problems, apparently Worcester Bosch say you can miss out the two port valve and second thermostat these days, but when i asked a few years ago they told me to rip out the low voltage three port valve and controls prefitted in one of their boilers and replace it all with 240 volt kit.

So assume the plumber knows what he is talking about and quote to wire up a two port valve after the three port along with two cylinder thermostats, I have a nice wiring diagram if needed.

Andy
 21 July 2013 06:16 PM
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primo

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I think Megaflo insist on a two port valve in addition to the three port for additional safety measure as mentioned. Although seem pointless installing a three port if you have to use one zone valve anyway. I had to do one like this a while ago and asked the plumber why he fitted three port instead of 2 port and he said it was because the kit he bought was cheaper and that happened to come with t three port valve!
 22 July 2013 05:58 PM
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Grumpy

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It must be an unvented cylinder that he's fitting. Since 2010 (I think, I did my G3 last Thursday so I've forgotten a lot obvs.) every source of heat into an unvented has to have it's own energy cut out. No probs with a S plan as cut the power to the 2 port valve and it shuts thereby cutting off the heat input to the cylinder. A three port parks in B (hot water) when the power is off so should the boiler limit stat also fail there is a posssibility of overheating. Hence the need for an additional 2 port. The preferred solution however is to convert the Y to an S.
 22 July 2013 07:52 PM
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SKElectrical

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sorry but my internet hasn't been working.

http://www.google.co.uk/url?sa...7-Qe5F3HAu5F5qst2a96A

page 5...
"The Energy Cut Out valve is an essential part of the safety requirements for indirect mains
pressure cylinders and should be installed on the primary flow to the cylinder with port 'B'
(embossed on side of valve body) to the cylinder. The valve will open and close on receiving a
signal from the cylinder thermostat. No further control is required for the hot water in a two zone
valve system. This valve must also be used in a flow share (Y Plan) system, in conjunction
with the mid-position valve, to act as a safety cut out valve.

The cylinder thermostat controls the temperature of the hot
water and also acts as an emergency cut out in the event that
he boiler temperature controls fail. The cylinder thermostat
s fitted into the pocket labelled "Store Temp Control" in the
cylinder, and should be connected to operate the energy cut
out valve in accordance with the wiring diagram for the
scheme being installed (see pages 11 and 12)."
 23 July 2013 09:54 PM
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SKElectrical

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I'm looking for a heating controls that control BOTH heating AND hot water....
a wireless version.

Any ideas? does one exist?
 23 July 2013 10:17 PM
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primo

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 23 July 2013 10:31 PM
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alanblaby

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Originally posted by: SKElectrical

I'm looking for a heating controls that control BOTH heating AND hot water....

a wireless version.


Wireless for both the room and cylinder stats?
Honeywell do one, but it is usually a special order for the cylinder stat - it is rare to fit a wireless one, but, just by chance I've been looking for one this week.
Danfoss are more common, even Wickes stock theirs. £130ish iirc for the 2 stats and base station.
 24 July 2013 10:54 PM
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sparkyaj

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Check out the water regs. If more than one heat input will be put into the immersion then it should have a primary isolator to shut down the flow from the boiler usually interlaced with boiler cutout. This is more frequently seen in solar thermal installations. A few boiler manufactures I have come across recently have specified this to prevent the boilers from over working should a fault condition develop.

Hope this helps a little.
 25 July 2013 05:16 PM
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SKElectrical

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Joined: 01 February 2009

I'm very surprised that the heatmiser is cheaper than its competitors
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