2-port and 3-port CH valves

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.
Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?
Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?
I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?
The pages I read suggested connecting the orange wire (only B port
open) to the pump. I'm sure I have misunderstood because if that's the
case what switches the pump on when you use port A only or A and B?
There seems to be some controversy: should CH be port A or port B, and
why should it make any difference? Is it that the valves fight against
a spring and that as long as the B port is open the mechanics are
fighting against the spring?
Is the idea that CH is on port A which is unenergised and the HW is on
port B, the theory being that the HW will warm up quickly so that the
valve is not energised for long? If so, does this mean that using
2-port valves is more energy inefficient?
Reply to
In article , Sam writes:
Also, with a 3-port valve you always have an open path for anything like pump run-on timers. With 2-port valves, you may need to make special provision for this.
It can be. Depends on size of house and usage patterns, and how long it takes to heat up and retain that heat.
A 3-port is always open somewhere. It has a built-in switch to signal the normall closed side being open. I believe there are standard wiring diagrams for the different Plans on the web.
I think it's usually H/W on A and C/H on B. This is to fit in with the standard wiring diagrams. Turning it round the other way might require addition of non-standard parts such as relays, and confuse the hell out of anyone coming to repair it.
I use a 3-port valve to switch separate upstairs and downstairs heating zones. I put downstairs on A and upstairs on B, on the basis that if it broke I can still heat downstairs, and that indirectly heats upstairs to some extent. Also, downstairs is heated more than upstairs, so the valve spends more time powered off than powered up with the synchronous motor stalled.
Reply to
Andrew Gabriel
In an earlier contribution to this discussion,
The actuator of a 3-port valve has more components (extra microswitch, diode, etc) than the 2-port equivalent and is more prone to failure. Mine last about 2 years on average. Because they play a strategic role in the control of the system, their failure can have a more profound effect, and is sometimes more difficult to diagnose. They also have the disadvantage that they can only control 2 zones - usually one HW and one CH - whereas you can have multiple zones with 2-port valves just by adding more valves. 3-port valves have the *advantage* that they always provide a flow path (unless *all* your radiators are fitted with TRVs) - so you're less likely to need a by-pass circuit to deal with the pump over-run phase, if required by your boiler.
It is certainly worth it if there are longish periods when you only want to heat part of the house, and provided the pipework lends itself to a split of that sort. [I can't do it because I have solid floors downstairs and the down rads are fed from a single shared circuit which runs between the floors.] If you *do* go for multiple zones, then it answers your first question, 'cos you'll need 3 x 2-port valves to provide 2 x CH + 1 x HW zones.
It needs to be wired according to the wiring diagram for Y-Plan systems - see the Y-Plan section of
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In either the HW-only or HW+CH (position) the boiler and pump are fed from the timer's HW output, via the cylinder stat. In the CH-only position, they are fed by the actuator's orange wire output which is internally switched to the grey wire input.
My Danfoss valve has CH on A and HW on B, and wouldn't work properly if connected the other way round. I imagine that other makes are the same for the sake of standardisation. The actuator's motor moves the valve in only one direction, with a spring return to move it the other way. When unpowered it sits in the B (HW) position. The valve is only drawing power in the mid and CH-only positions - unlike 2-port valves which draw power whenever they are open. This means, for example, that a 3-port valve may not move all summer when only the HW is being heated. Whilst this might save energy, it also increases the risk of the valve seizing up - so 'exercising' it every now and then is a good idea.
Reply to
Roger Mills
On 10 Jan 2008 14:56:47 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew
Thanks for your reply. I see below that you have two zones. Can you tell me more about your set-up and usage? What should I do to work out whether I should do the same? I'm in a 1970's build so no modern-day super insulation!
The diagrams I found confused me! I hadn't appreciated the always open aspect until you said. I assume the pump needs to switch on when either thermostat calls for heat. Do you just run wires from both 'stats to the pump?
That's what the FAQ says IIRC but I whilst googling I found reference that one manufacturer prefers you to use HW on B because this means the valve is energised for a shorter period if I understand correctly.
Really? How does this work? You heat downstairs in the early evening and then switch to heating the upstairs at night?
Thanks again.
Reply to
"Sam" wrote
I had my heating system upgraded last year. 1970s detached house - 4 bedrooms. Decided to have the upstairs and downstairs zoned separately.
Advantages: previously the whole house was heated from 3:30pm when the kids return from school - now downstairs from 3:30, upstairs from 7:30. Haven't got round to looking at the resulting gas saving although this will be enhanced by the new boiler that was fitted I guess.
Disadvantages: Hallway is noticably cold (obviously) due to cold air "falling" from landing. The installation is a bit more complex when considering future maintenance.
Also have a look at the location of the pump in a new system. My previous set-up had a pumped return rather than pumped flow which leads to quite a bit of additional pipe work being required.
Reply to
In article ,
My first one did some 20 years and was replaced in '99. Replacement still fine. Both Honeywell.
Depends what you mean by open - because some types are always open. They have a micro switch to prove the state.
Wiring diagrams here - or do a search for others offering similar.
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Reply to
Dave Plowman (News)
That's not very long. It's not very reassuring.
Couldn't you have a 3-port for CH or HW, with the CH port connected to another 3-way for upstairs (A), downstairs (B), or both (A+B)?
For more than two zones, I see your point.
Someone else mentioned this "pump over run". What is it and how do I find out if I have it?
I think taht's the point I was missing: I hadn't realised that in addition to the orange wire they were also connected to the stat. I knew there had to be two connections!
Something that escaped me until I thought more about it was this:
I thought what if the valve is set to CH+HW but the tank fills up, won't the pump stop pumping? When I thought more I realised that when the stat is satisfied it turns the valve to CH only.
Thanks again.
Reply to
On 10 Jan,
I did that for about 5 years (together with a preceding one for HW/CH) until I got fed up with replacing micro switches.
Since changing to 3 two port valves I haven't had to change anything in the last 8 years (although I should get round to fixing a slight leak on the spindle of one of the valves one of these days).
For some reason the micro switches in the 3 port valves seem much less reliable than in 2 port valves, perhaps the valves hunt slightly with mains volts when in the mid position. I can't think of any other reason.
Reply to
On the other hand, we've been in our house for 18 years and the 3-port valve is still working fine.
Reply to
In an earlier contribution to this discussion,
Not without a lot of complication in the wiring department, bearing in mind the way in which - unlike 2-port valves - some of the wiring is shared by motor driving and boiler/pump running functions. Far better to use 3 x 2-port valves which will probably cost very little more than 2 x 3-port valves. The 3-port valve is designed for one very specific application, and doesn't readily lend itself to departures from the standard Y-Plan setup.
Most modern-ish boilers - which hold relatively small quantities of water - require it. Old heavy cast iron boilers usually don't. When the boiler is in full flight and the room stat decides to turn it off, the flame is cut instantly but the water goes on getting hotter due to the residual heat in the metal parts. There needs to be a flow of water through the boiler for long enough to carry away this residual heat - otherwise the boiler literally boils. This is achieved by allowing the boiler to control the pump rather than controlling the pump directly by wiring it in parallel with the boiler. If your boiler needs it, there should be something about it in the installation manual. Also, if you look at the boiler's wiring connections, there will be a permanently live input - in addition to the switched live - and there will be pump connection terminals.
For pump over-run to work, there must always be a flow path open for the water to follow. A 3-port valve always has at least one port open. A 2-port valve doesn't - and all (2 or 3) could be closed when all demands are satisfied. You would then need a by-pass circuit - preferably using an automatic by-pass valve - to provide that flow path.
Reply to
Roger Mills
My boiler looks ancient and only has live and neutral, so I guess I'm ok? It's also oil rather than gas; does that make a difference?
In situations that require it, how is it achieved?
I've heard of these bypass valves. Do you also use them if TRVs are on all radiators? I've always left TRVs off the hall rad (thermostat) and bathroom (towel rad) hoping that would be sufficient for whent he other TRVs close. Do I need a bypass in addition or is that enough?
Thanks again.
Reply to
In an earlier contribution to this discussion,
I don't know much about oil-fired boilers - but imagine that some *do* need pump over-run. If yours is old, and holds a lot of water, it probably doesn't. Especially since it only appears to have a switched live.
Invariably the pump is connected to some dedicated pump control terminals on the boiler, and the boiler decides when the pump needs to run - quite independently of what the external timers and stats are doing. The actual logic varies from boiler to boiler. Mine has a thermostat and, in addition to running the pump whenever the external 'call for heat' demand is on, also runs it whenever the boiler temperature is above a certain value - until such time as it has cooled sufficiently. Some simply have a timer which continues to run the pump for a specified time after the demand is removed - similar to a bathroom fan remaining on for a while after switching off the light. As I said in an earlier post, the boiler needs a permanent live so that it *can* power the pump even when the external (switched live) demand is off.
From what you say, your boiler doesn't need a pump over-run - so the pump stops when the demand is removed, and the water doesn't need anywhere to go. Systems which have TRVs on *all* radiators (not recommended!) and which use a boiler which needs pump over-run may well need a by-pass - even when using a 3-port valve because in CH-only mode with all TRVs closed there would otherwise be no flow path.
Reply to
Roger Mills
In article , writes:
Funny, I see a few reports on here of unreliability of these things, but we've never had one fail in mine or any of about 3 other family member's systems yours truely ends up maintaining. They're all 3-port mid position units. Just checked one of them which is at least 8 years old and it claims to be a British Gas one (rebadged I'm sure, but don't know who from). One I fitted in a new system about 6 years ago was Landys and Steaefa and going very cheap as old stock. Don't know about the others as I've never had to pay them any attention.
In the system I designed, I don't use the microswitch as the valve is driven by a computer, not one of the conventional circuit arrangements. (I did use it to confirm the valve was working initially, but I needed that computer input back for something more important.) There is a second microswitch which is used internally to lock in mid position.
Reply to
Andrew Gabriel
On 10 Jan,
The ones I used were Danfoss HS3s now replaced (the heating ones) with HS2s.
I left the other one (HW/CH) for several years longer until SWMBO started complaining of the heating going off if the water was heating. I was then using it as a diverter, not using the mid position. However it seemed to be more reliable in that mode, but I've now replaced it (it started leaking IIRC) with one of B&Q's best(2 port), I'm not sure what make it was.
Reply to
Might be worth considering what sort of load you are switching with the microswitch. Often people don't bother fitting snubber circuits when they are controlling inductive loads. This can lead to premature wear on the microswitch contacts.
You could...
Most modern boilers will control the pump. As a result they have the option of running the pump for a period of time after the boiler has ceased firing. This helps extend the life of the heat exchanger and is a little more energy efficient since it does not leave the HE full of hot water.
Older systems with "dumb" boilers would probably have had the pump controlled directly from the valve. Hence as soon as the call for heat from the stat was taken away both the pump and the boiler would be turned off.
Reply to
John Rumm
A circuit that helps dissipate the big spike of voltage that is generated when you switch an inductive load. At its simplest it can be a metal oxide varistor suppression type device (cheap at maplin).
There is an example of a more sophisticated circuit used for protecting the relatively delicate contacts of a reed switch shown here:
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Reply to
John Rumm
In article , John Rumm writes:
A MOV is the wrong device to use for this, as the energy it absorbs uses it up, until it runs out of capacity to absorb any more and stops working. It's good for one-shot protection or a small number of smaller incidents, but not for something which is routinely expected.
All you need for a contact snubber is something which allows the current to carry on flowing when the contacts open until the reactive energy is safely dissipated. This is normally done with a resistor which allows current flow and dissipates the energy, in series with a small capacitor which blocks the current flow at 50Hz.
e.g. [fixed width font]
| | --/\/\/\---| |-- | | | | | | | / | | / | ---------/ -------------
This is so common you can buy the resistor and capacitor combined in one component (looks like a capacitor, e.g. Maplin part RG22Y).
protecting anything, but there isn't anything in that circuit which needs protecting with a snubber anyway (except possibly the triac, but a snubber across a triac is for a completely different reason).
Reply to
Andrew Gabriel

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