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Heating timer |
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| message from Can2002 on 20 May 2004 |
We have a conventional gas boiler (Potterton Netaheat) with a hot water
cylinder. The rather aging timer only allows us to switch on the central
heating if water heating is enabled.
I'm trying to discover whether this is a limitation of the timer or whether
the system itself ties central heating to water heating.
Thanks in advance for any help!
Regards,
Chris
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| Dave Plowman replied to Can2002 on 20 May 2004 |
To be able to separate them, the hot water primary must be pumped and be
controlled by electrical valves. If it's just thermo circulation, it will
be on any time the boiler is. In this type, the pump only works the
heating, so if it's not running, no heating.
IMHO, if you do have this elderly system it would be worth converting to
fully pumped - not that expensive a DIY task and well worth it - your hot
water will heat much more quickly.
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| John replied to Dave Plowman on 21 May 2004 |
I'm not disputing the benefits of a fully pumped system but you have
completely overlooked the "C-plan" system which can give independant hot
water/heating control with a gravity primary system
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| Lurch replied to Can2002 on 20 May 2004 |
Most probably a system limitation. If you're airing cupboard has no
heating related equipment in it other than the cylinder then you're
stuck with it the way it is unless you alter the pipework and add a
few components.
If you have an airing cupboard with at least a pump, a valve and a
cylinder stat then it's probably a switch on the back of the clock
that needs switching from 10 to 16, or gravity fully pumped.
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| Can2002 replied to Can2002 on 21 May 2004 |
Thanks for the responses guys,
I've had a good look in the airing cupboard and am not sure whether what I
have meets your descriptions. I'm going to try to describe the bits in
there!!
The cylinder has three entrances at the bottom, 1/3 up and at the
top-centre. The pipe (22mm) coming out 1/3 the way up connection goes into
a 90 degree connection and then up about 1.5 feet. it then goes into a
connector that splits into 15mm (vertical) and 22mm (horizontal). The 15mm
side connects into what looks a bit like a pressure release valve (brass
barrel with a red plastic thumbscrew on top). The 22mm end of the connector
goes into a fist-sized unit into which a three core power cable runs from
the timer junction box. There are two 22mm connection leaving this box, one
of which is below and feeds into what defintely looks like a pump, which is
once again connected into the timer junction box via three core power cable.
The other side of this pump feeds a 22mm that disappears into the wall. One
other point regarding the pump is it has a switch with three settings (I, II
& III - currently set to III).
Apologies if the above is complete gibberish, but does this shed any light?
Regards,
Chris
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| Set Square replied to Can2002 on 21 May 2004 |
It sounds as if you have a fully pumped system, using a 3-port valve (either
diverter or mid-position). See whether the following description is
consistent with what you have just said - albeit in slightly different
terms:
"Hot water is pumped from the boiler to a 3-port valve located above the
pump. This valve has one inlet (connected to the pump) and two outlets. One
outlet is connected to the heating coil inside the hot water cylinder. The
other outlet directs hot water to the radiators." Does this fit?
If so, is there a thermostat strapped to the hot water cylinder, allowing
you to control the temperature of the hot water? If so, you have all the
right bits to allow independent control of hot water and central heating -
it's probably just not wired up correctly.
Take a look at the different arrangements described in
http://content.honeywell.com/uk/homes/systems.htm
Depending on whether your 3-port valve is a simple diverter valve (i.e.
either hot water or heating, but not both together) or a mid-position valve
(as above but with the added capability of having hot water and central
heating on at the same time) you could potentially have either a W-plan or a
Y-plan system.
Both of these give you the possibility of having central heating without
domestic hot water providing:
a) the programmer permits it (may be necessary to remove an internal link in
the programmer)
b) the cylinder stat is the changeover type - with a "hot water satisfied"
contact
c) (in the case of Y-plan) the programmer has a "hot water not required"
connection which is correctly wired up.
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| Can2002 replied to Set Square on 21 May 2004 |
Following it from the other direction what you suggest does indeed fit! To
experiment I switched the CH off (both HW & CH were on at the time) and
could hear what sounded like a small motor in the valve mechanism. I'm
going to leave it a while and then see if what I now believe is the radiator
feed gets colder!
There is indeed a thermostat on the cylinder.
Is there an easy way to tell? I guess one thing I noticed was that with the
system running both pipes leaving the valve are very hot, which implies it's
the latter of the two you describe above. The one thing I do recall when we
moved in was that the thermostat on the cylinder was set very low and we
found that the CH did not get very hot. When I upped the thermostat setting
on the cylinder things semmed to improve, which makes me wonder!
Thanks for all your help!
Regards,
Chris
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| Set Square replied to Can2002 on 21 May 2004 |
If the valve has a model number on it, someone can probably tell which type
it is.
If you select CH and DHW at the same time, and turn both stats up, and if
both lots of pipework get hot (too hot to touch!) at the same time, it's
very likely that you've got a mid-position valve (Y-plan).
If the radiators only get hot when the hot water stat is calling for heat,
I'd put my money on a wiring error. There *must* be 3 wires (in addition to
any earth wire, if applicable) connected to the cylinder stat. If there are
only 2, it is definitely wrong.
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| Martin Angove replied to Can2002 on 21 May 2004 |
Despite what others have said, it is possible to have a fully pumped
system with a motorised valve and yet a controller which only allows HW
or HW+CH. I know; I've just ripped one out of mum & dad's house after
some 36 years.
It was a mechanical timer (with pegs) and two rocker switches. One set
off/on/timed, the other HW only or HW/CH. The primary reason for ripping
it out was that the motor had suddenly become very loud and clicky. The
secondary reason was that it hadn't actually worked for <n> [30>n>10]
years. Instead mum & dad would get up to a cold house, go downstairs to
the "Water Heating" switch in the cupboard under the stairs and turn it
on. HW had priority, so if the cylinder was cold it took 30 minutes
before the radiators started warming up.
I replaced the thing so that HW and CH were separately timed. It
involved a complete rewire of the system and (oddly) turning the
motorised diverter valve around 180 degrees. I also had to add a relay
because the two timers were SPCO only and the two "on" situations are
pump only and pump plus valve.
Because it is a diverter and not a 3-position, HW still has priority,
but with both systems timed it is possible to stagger the on-times in
order to ensure you get heat when needed. I used 1 HW timer, 1
timer/stat, 1 "wiring centre" (bit of chocky block in a box) and 1 240V
DP relay in a box. It's not the system I'd install if I were doing this
from scratch, but it was a relatively cheap and simple upgrade and has
made a *big* difference to the ease of use of the system.
Hwyl!
M.
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| Lurch replied to Martin Angove on 21 May 2004 |
I'd just like to make it known that that's what I said, in different
words.
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| Ro replied to Martin Angove on 22 May 2004 |
I am planning a similar installation, sort of, with a programmer
controlling my immersion, and my electric central heating (bizarre, I
know). What relays did you use? i was looking at some contactors, but this
would entail adding them to the consumer unit, and I am not that brave.
Ro
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| Lurch replied to Ro on 22 May 2004 |
Well, your immersion can be controlled from a immersion heater timeswitch, these
are rated at 16A usually.
What is the rating of the electric heating? You still need to add the relays to
the wiring somewhere, a relay and a contactor are, basically, the same thing. If
you are unsure of how to connect up a contactor then a relay isn't going to help
you much, if anything they're probably more involved in that you need to make
your own enclosures for them.
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| Ro replied to Lurch on 24 May 2004 |
What I'm planning to do is use a 3 channel programmer with 3 contactors or
relays to control the immersion, the heating unit (rated 20A) and a heated
towel rail.
Currectly are all controlled separately with timeswitches, but they don't
have advance or boost facilities, and I have had a few big bills
attributed to having left either one on for a prolonged time.
I would be happy to use the relay option, but reckon the the contactors
wired directly in the comsumer unit, in series with the MCB for each of
the 3 circuits would be a more professional, and probably safer option
that making ny own enclosure with relays.
I am a bit worried about messing eith the consumer unit. I would need the
electricity supply cutoff prior to adding the contactors, wouldn't I?
Ro
On Sat, 22 May 2004 16:23:52 GMT, Lurch <theoriginallurch@tiscali.co.uk>
wrote:
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| Lurch replied to Ro on 24 May 2004 |
Definitely. I would fit DIN rail mounted contactors and the associated control
circuit wiring into a seperate enclosure, like a blank consumer unit.
Er, yes, but not all of it. Are you sure you should be doing this?
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| Ro replied to Lurch on 24 May 2004 |
I'm not really. I am pretty proficient at most DIY electrical stuff, and
have wired lots of bits like new sockets, lighting etc, but have not
ventured to the consumer unit yet. I assumed that any work done on the
consumer unit would necessitate the supply being turned off? If I take the
cover off, there will be an exposed live feed, I would have thought?
I'm confident I would have no problems with the actual wiring, but I would
be worried about working on it while at least some of it was live. Is
there a safe way to fiddle with the MCB etc on the same board as the main
switch?
I'm probably going to get an electrician to do it for me.
Thanks,
Ro
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| Ro replied to Ro on 25 May 2004 |
Thanks for the offer. I'm actually in Ireland.
I had a look at the consumer unit with the cover off. It looks less scary
now. I can see the rather large fat red wire bringing in the feed, and the
main switch.
The rest is pretty straightforward. i just need to wire each contactor in
series with the appropriate MCB. There's actually an old mechanical
timeswitch with pegs, (pegs missing) which I can get rid of also, which
will simplify things a lot.
Just ordered the contactors. Will give it a go as soon as they arrive.
Ro
On Mon, 24 May 2004 23:04:18 +0100, Martin Angove
<MJAngove@tridwr.demon.co.uk> wrote:
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| Martin Angove replied to Ro on 24 May 2004 |
My parents are all gas, so the relay was only switching a couple of amps
for the pump, the valve and the gas valve on the boiler. I bought
something suitable with a plug-in base and put it on a bit of DIN rail
in a little box, mounted next to the wiring centre.
If I had heavy electrical heating loads I would certainly be looking at
contactors as they are almost bullet-proof, though there are undoubtedly
relays available which will cope with 16A or so - one per heating device
perhaps. It'll all have to be mounted though.
Why do your contactors have to go into the consumer unit? Can you not
wire up a separate "contactor box" somewhere nearby? An empty CU with
100A switch, and split the incoming (from the meter) with the
appropriate connector box perhaps?
Hwyl!
M.
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| Martin Angove replied to Ro on 24 May 2004 |
Not usually, unless it's quite old. Most modern-ish units have all the
permanently live stuff quite well insulated - that is the incoming
before the big red switch, and certainly with most MCB units even the
live after the switch has a certain amount of protection such that you
really have to *want* to touch a live part to be able to.
In other words, switching off the big red switch will usually (but take
a look to check first) isolate the supply sufficiently for you to have
to try very hard to touch anything live with the lid of the unit off.
As above. Usually simply turning the main switch off does the trick.
Just try not to stick a bare metal object into the screw terminals
holding the incoming cables eh?
If you're in the Caerphilly area I know a good one :-)
Hwyl!
M.
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