Over-controlled CH - explanation of operation please?

Discussion in 'Getting Started FAQ' started by Dr_alan_c, Feb 4, 2024.

  1. Dr_alan_c

    Dr_alan_c New Member

    Hi, new here and not sure where best to post a question about CH (leccy or plumber?) - moderators please move if necessary. Also I don't know the right terms - e.g. how to differentiate between electrical circuit and water circuit except by context? So apologies if my writing is confusing.

    I had CH installed in a house where previously we were all-electric. So for HW we have an indirect system (the boiler heats the water in a cylinder which has immersion heater ports), plus two circuits for upstairs and downstairs radiators.

    The three (water) circuits are teed off a single output from the boiler (which is a Vaillant EcoTec plus 630) and controlled by motorised 2-port valves.

    I specified radiator thermostats as well as room thermostats (one downstairs, one upstairs) and I wanted a programmer with separate control of on and off times for each of the three circuits (HW, CH down, CH up); however the installer put in a Drayton LP522 which only caters for two separate circuits (Ch and HW). So it has too many controls - in reality we could use either the radiator stats or the room stats to control the system for comfort. The way we use it is to use the room stats as "on/off switches", and turn up and down the rad stats when we go into or come out of rooms. Hey ho. It works.

    My question is this: how is the electrical system arranged so that the programmer can open and close the valves at the programmed times, and the room and cylinder stats can also control the heating? If the room stats were just in series with the programmer output to the motorised valves wouldn't they only be able to stop the valves from being operated, by interrupting the electric supply to the motor? It suggests to me that if the room is warm at the time when the programme should be turning the heating off, the programmer won't be able to shut off the circuit (or if the stat is "normally closed", the equivalent result would be that when the room is cold, the programmer won't be able to open the circuit when the system should be turning on).

    I'd be glad to hear your collective insights into how this system should be wired, and any changes you might recommend. [edited for spelling]
  2. Hausfix

    Hausfix Screwfix Select

    Hopefully I’ve understood your description well enough to provide some sort of relevant reply.
    I’m assuming that you have three in number of 2 port motorised valves? (1 for the HW and 2 for the CH, up and down?)
    The basic control works like this: The programmer will first send out a signal to ‘call for heat’ at the time set. Then this signal passes to the room thermostat, if the ambient temperature is lower than the stat is aiming for, the stat will pass the signal on to the zone valve it is wired to. The zone valve will open to allow hot water into that circuit, a micro switch in the zone valve will then pass the signal to the circulation pump and the boiler. The boiler will then fire up to satisfy the demand for hot water.
    The radiator thermostats act independently, and don’t have a say in whether the boiler switches on or not, all they do is restrict the flow of the hot water into that particular radiator.
    If the system is set up correctly, decide when you want the heating to be operational, set the room stat to the temperature you would ideally like in that part of the house, then you can dial down the radiator thermostats for the rooms you don’t use or think are too hot.
    The Drayton LP522 you’ve got, isn’t going to be able to control two heating zones however. That needs to be changed for one that’s capable of that function. Alternatively, you could change the two room stats to programmable units and leave the Drayton LP522 set to CH constantly ‘ON’ and the HW side set to run at the times you require. Wired correctly, the programmable room stats will take proper control of the the two independent heating zones.
    I’ve also made the assumption that the radiator stats don’t have wiring that runs to the wiring centre, just battery operated and moreover, not connected to a Wi-Fi controlled network.
    Last edited: Feb 4, 2024
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  3. LearnMore

    LearnMore Well-Known Member

    If you haven’t got what was specified, why not get the installer back to correct it? Explanation of electrics has been given above. It depends if it’s been wired correctly for any changes to happen.
    Hausfix likes this.
  4. Dr_alan_c

    Dr_alan_c New Member

    Hausfix, Many thanks for your reply. It's a conventional(?) system, there are no wifi-enabled or other intelligent devices. Just to cover all the bases I'll set down as many details of the system as I can:

    Vaillant EcoTec plus 630 boiler.
    Three water circuits: upstairs radiators, downstairs radiators, hot water cylinder.
    Three two-port valves - no manufacturer's markings; the motor inside is simply marked 230V 50Hz 4rpm. (These don't seem to be very good - I've had one of them replaced twice in three years.)
    Drayton LP522 timer / programmer.
    Drayton TRV4 valve on each radiator (pure thermo-mechanical valves, no electrical or wireless connections).
    Honeywell L641A thermostat on the cylinder. Hard wired to a junction box near the LP522.
    Honeywell T6360 in upstairs hallway. Hard wired to a junction box near the LP522.
    Another Honywell T6360 in downstairs dining room - position selected as being less likely to be affected by independent heat source in living room (log burner). Hard wired to a junction box near the LP522.​

    As I understand it, the boiler is capable of supplying CH and HW independently; however the three circuits are all connected together upstream of the zone valves and the boiler display panel only ever indicates a heat demand from CH.

    Although the Drayton LP522 clearly only has two channels, it does somehow seem to be able to control the three zones - but the downstairs and upstairs zones clearly always have to be on or off together; so the separate room theromstats must be controlling the individual zone valves to prevent the flow upstairs when we are using downstairs. Your description of how the system operates is interesting; I hadn't realised it was so clever. I had assumed the room stats were simple switches, connecting or disconnecting. I can see how, if instead they use signals, and power is supplied direct to the zone valves, the zone valve motor can "know" whether it is being told to open or close. Do you know the voltage levels, etc. that are used?

    They way you suggest using it is more or less what we do, except that we don't rely on the room thermostats to control the temperature as we don't want to be heating the dining room unless it is in use. So our main means of control is the radiator thermostats.

    LearnMore: I guess you're right, I should have made a fuss at the time but I assumed I didn't understand what i've been given - which come to think of it was true enough. I would have liked to have separate on and off times for upstairs but it really isn't a great bother; and now that 3 years have passed I don't think I ccan complain. However, I would like to know whether it will be possible to change the controller if I decide I need to.
  5. Hausfix

    Hausfix Screwfix Select

    The Honeywell T6320 room stats are indeed the type of 7day programmable stats that I suggested, so it appears you have all the right basic equipment to run the system as desired. It will be now just a case of checking the wiring centre, (the junction box located by the LP522) to determine if it’s been correctly wired. To the uninitiated, the wiring inside can seem bewildering, but one you understand the logic process, it’s actually quite simple.
    I used the term ‘signal’ to simplify the explanation, it is in fact just a 240v live supply that is routed by a series of switches, the switches being relays within the controllers, stats and zone valves. Nothing more sophisticated than that!
    The zone valves have several wires leading to and from them, a permanent live and neutral in, a switched live wire from the stat to activate the motor, then once the motor has fully opened the valve, a micro switch will then send 240v Live power down the 4th (orange) wire to activate the boiler. In addition to these 4 wires is an earth wire too.
    If you can open the cover of the wiring centre, take a photo of the wiring inside and post to this thread, one of us just may me able to spot an issues or confirm if all looks good, but this is a long shot.
    It does appear from your description that you should leave the CH side of the LP522 set to permanently ‘ON’ for your set up to work correctly.
    The Vaillant Ecotec 630 is a system boiler as far as I am aware, so will only output hot water from one outlet. It’s up to your plumbing and control gear to handle where that water is directed, be it HW or CH. The boiler won’t be controlling one or the other.
    Last edited: Feb 4, 2024
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  6. Dr_alan_c

    Dr_alan_c New Member

    @Hausfix: thanks again; but are you sure about the room thermostats? It's Honeywell T6360 and there's nothing in the instructions about programming ;-)
    I tried and failed to upload a picture of it; anyway it has a simple analogue dial for set temperature between 10 and 30C and that's all. Can you enlarge on the zone valve control at all? It makes sense that if it has its own permanent supply (live and neutral) then it can operate when the switched live from the stat is energised; but how does it operate in the other direction? Does it have a change-over relay, perhaps?
    If I can figure out how to upload a picture I'll post the innards of the zone valve and the wiring centre.
  7. LearnMore

    LearnMore Well-Known Member

    What do you mean, in the other direction? A Honeywell T6360B should have a L,N,E and switched live.
  8. The Happy Builder

    The Happy Builder Screwfix Select

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  9. Dr_alan_c

    Dr_alan_c New Member

    I was referring to the direction the zone valve motor has to turn in - I assume it turns one way to open the valve, and the other way to close it. If the feed comes stright from the Honeywell T6360, with a single switched live line, then how can it reverse direction?

    My assumption is that the T6360 energises that swithced live line when the air temperature is below the set point; then this can power the zone vale motor to open the valve and supply hot water to the zone... but when the air temperature rises, I assume the switched live is isolated. So how does the zone valve get closed?
  10. Dr_alan_c

    Dr_alan_c New Member

    That's a really useful reference, many thanks.

    In my case I guess the Building Regs were assumed to be not relevant as it was an installation into an older property; but I requested zone control and radiator thermostats. But I see that the Regs apply when:‘significant works’ are carried out on a controlled service (i.e. the heating system). Hmm, I would assume that a complete new installation counts as "significant works"!

    In general, it looks as though the installation meets the regulations with:

    (although I don't know whether there's an automatic bypass valve). But I would have preferred a twin zone programmer.

    The Honeywell data for V4043H zone valves says that the control is just one way (energise the motor to open; closure uses a spring). But that would mean the motor is energised for hours at a time in the stall condition (i.e. when the valve cannot be turned any further). Sounds like a recipe for failures? But I also see other suppliers offer valves with "two point" control and their details show that the motor is only powered when the valve is operating (opening or closing). I think that's the type I've got but they have no manufacturer's markings on the visible faces. So I'm still in the dark about the details of the wiring.

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