Replacing Horstmann 425 with Hive (again)...

[phmode]

...but just not yet.

I have another thread running all about whether my Hive system will work when I take the whole shebang to a new address. So, that house move has now happened (it's a friend moving house, not me) and this is where my problems start.

The 'new' house has a Worcester Greenstar Ri boiler, pumped CH and HW with a mid-position valve and a Horstmann 425 Diadem programmer which clearly has a ghost in it.

As a prelude to fitting the Hive, I did the usual wiring diagram for the house to plan out where everything is, physically and electrically. The boiler and programmer are in the garage (along with a frost stat) with everything else bar the room stat in the airing cupboard with the cylinder.

The 'wiring centre' in the airing cupboard is a fairly conventional set up...

...with the MPV coming in on the left, cylinder stat from bottom left and pump from bottom centre. But no sign of the room stat connections.

When I removed the programmer from the backplate I was faced with this...

...and this is where I get really confused.

Apart from not being able to see what is connected to where (but logic and a meter will show that in good time) there is no wire connected to terminal 3, HW OFF. It hasn't come out or been cut, it simply was never there as the terminal screw is fully in. Being winter I have no intention of opening this rat's nest and leaving the lady in the cold, until I have a day or two to understand it fully. The cables at the top are 'labelled' from the left, Pump+Boiler+N, Valve, F(Frost Stat) & Stat(Room Stat). Cables at bottom are Boiler on the left and mains on the right.

My question is why was this system wired like this (no wire to 3) and what is happening if HW OFF is NOT being sent to the grey wire on the valve? Permanent hot water when the CH is on I guess. Having a mixer shower, and being in a new-home cleaning frenzy, the lady needs the hot water, just not permanently.

Of course, being a mere DiY'er, I have probably missed something obvious here...

Your thoughts gentlemen and gentleladies?

 

[stem]

A Hive Dual Channel receiver can replace the Horstmann Diadem

Horstmann

Hive Dual Channel

From the above diagrams, and assuming that the system is presently working correctly, the wires move from the Horstmann terminals to the Hive terminals that have exactly the same function as follows:

Diadem E = Hive Earth Tether
Diadem N = Hive N
Diadem L = Hive L
Diadem 1 = Hive 3 (Hot water on)
Diadem 3 = Hive 1 (Hot water off)
Diadem 4 = Hive 4 (Heating on)

There shouldn't be a wire in Horstmann terminal 6 (heating off) and don't worry about the links to the Horstmann terminals 2 and 5. Hive has these already made internally.

The room thermostat should normally be connected to the white wire of the motorised valve, which I have circled in purple below:

Therefore it would be usual for the yellow wire in the same terminal will be the 'switched live' from the room thermostat (you will have to check this)

It's difficult to see properly in the photo, but it appears that the red wire going to the terminal circled in green is from the same cable as the aforesaid yellow, if so, that is likely to be the 'live supply' to the room thermostat wire (again you will have to check this).

If after checking, you find that my assumptions are correct, and the cable at the top of the junction box is the one going to the room thermostat, it should be disconnected completely and removed, and then the white wire from the black cable of motorised valve should be put in the terminal in place of the removed red wire.

If you have any doubts, or any of my assumptions aren't correct, don't proceed and post back. It looks that the Horstmann may be being used as a junction box in addition to the circular junction box, so you may find the reality is different to the norm. (if there is a norm)

If it were me I would be stripping everything out and starting from scratch with this one, at least with the connections but perhaps reusing some of the installed cables.

You are right about the 'HW off' from the Horstmann terminal 3, it should be connected to the grey wire of the MV, I can't see the photo clearly enough. Are you sure its not hidden in the rats nest.

 

[phmode]

Hi Stem and thanks for the rapid and detailed reply.

I understand the Hive replacement as I have one I installed on my oil boiler and the one I will be installing in the friend's new place was originally installed by me in her old home. Also, I have read the original thread on the Horstman and just wish that my back plate were as simple as the op on that thread.

Here is a better photo of the rat's nest...

...and you can see that terminal 3 is empty and the screw was down tight.

As you say, stripping back and re-purposing the cables is the best solution. I never like to strip out things like the room stat cable in case future owners want to go back to a simple system so that will be re-routed into the airing cupboard, isolated and labelled. Also, I have always installed Lifestyle Wiring Centres in all my homes as it makes future changes much more straightforward.

However, between the Valve cable and the PumpBoilerN cable I should be able to get everything back to the airing cupboard with nothing more than a simple piece of chocolate block in a patress box to get the boiler connection sorted.

It's going to have to wait a while but the programmer is playing up intermittently so there is a certain urgency to get it done. Thanks again, Brian

 

[ericmark]

I see your point, there should be a wire from the green/yellow to grey going to the NC on the programmer and this is missing. This means you can't turn DHW off at the programmer, however many programmers had the option to work with C Plan where there was no option to turn off DHW, so suppose if the dip switches are selected correctly in the programmer it would work, you had 10 instead of 16 programs.

So will the existing programmer allow you to turn off DHW?

See page 5 Gravity if set that way it would work. Has it been set that way, and can Hive also be set that way?

 

[ericmark]

I seem to remember on a previous post talking about the three versions used with the C Plan, no tank thermostat or motorised valve, it relied on pump running or not running to have CH + DHW or just DHW, next version had a thermostat on the tank so in summer the central heating boiler only fires up when required, and next was also a motorised valve so you could control the DHW temperature to a lower setting summer and winter, and turn off DHW, all called C Plan as all used gravity to heat DHW.

I know yours is Y Plan but using the middle C Plan settings on the programmer it would work without that wire on the NC terminal, what the big question is can Hive be set that way, as when this subject was raised before I was told if set to gravity then when central heat is on it always switched domestic hot water on, I thing this would work, but wait for @stem see what he says.

 

[phmode]

I see your point, there should be a wire from the green/yellow to grey going to the NC on the programmer and this is missing. This means you can't turn DHW off at the programmer, however many programmers had the option to work with C Plan where there was no option to turn off DHW, so suppose if the dip switches are selected correctly in the programmer it would work, you had 10 instead of 16 programs.

So will the existing programmer allow you to turn off DHW?

See page 5 Gravity if set that way it would work. Has it been set that way, and can Hive also be set that way?

To answer your last question first, no it is NOT set to gravity with the switches interlinked. As for the Hive, no it can't but before that goes in I will have sorted the wiring to give 'normal' connections to all 4 (OK, 3) switching terminals.

You also mention DIP switches. There is nothing in the programmer installation instructions that I can see that talks about DIP switches and I can find no obvious evidence of them on the programmer.

I'm struggling with this because the system is 50 miles away from me and I won't be back there till next weekend. I also mentioned that the programmer had a ghost in it, more of this later...


Yesterday I went over during the day to do some more visual checks of the wiring to the room stat etc. I removed the programmer to take the photos and then re-fitted it, reset the dial to the correct time by cycling the dial through all four switching positions, checking that event 2 was showing in the status window, which was correct as the time was between events 2 & 3 and that both switches were set to TWICE and then I left before the evening ON period.


That evening, the heating failed to operate on either HW or CH despite both stats calling for heat and the switch status indicator showing 3, evening ON event. At this point, being cold, the friend switched both sides to ONCE and the boiler fired and worked normally on both CH and HW.


After the last OFF of the evening, she turned both selector switches back to TWICE ready for this morning.


Later last night, after she set both switches to TWICE, I was talking her through the process of dicovering whether she could in fact turn the HW OFF. I had her leave the CH on the TWICE setting but with the HW set to OFF.


This morning the system failed to fire up despite the CH indicator light on the programmer being ON, the time being correct on the dial and the switch status window showing that the last switching event was set by tappet 1, the morning ON switch. She left the system until after the morning OFF event and then called me to report the results. She also set both switched to 24hrs and the system fired on both CH and HW. She has now given up in disgust and is spending the weekend with me, my log burner, the oil boiler and the hot shower...so heaven knows what the system is up to in her absence.


I mentioned earlier that the programmer has a ghost in it. About a week ago, having only been in the house for a few days (with the HW and CH both left on 24hrs by the previous occupants, unbeknown to my friend) we turned both switches to TWICE and set the ON/OFF periods to her requirements. That evening, the system didn't fire. When I investigated, the time was now wrong, and every time I tried to reset the time by rotating the dial, the status indicator sequence went from 1 to 2 to 4 and then to 1 to 2 and 4 again. After a few frustrating revolutions the sequence came back to normal and the system then worked normally with both switches set to TWICE until my intervention yesterday.


The manual does talk about the switch state indicator getting out of sequence with the actual tappets and assures me that one revolution of the dial will fix things. So, I am assuming that the Programmer has a quirky failure mode which doesn't bother me because as soon as I understand the wiring set up it is going in the bin and the Hive is going in.


So, to answer your and my original question about whether we can turn the HW OFF, the simple answer is we don't know but we will be testing it again sometime soon.

Thanks again. Brian

 

[ericmark]

Some of what you have said makes sense, if you look at the internal wiring of a mid position valve

the supply to the boiler is in two positions through the tank thermostat, the first thing to remember grey is made live when DHW is not wanted, and it seems if DHW is on at programmer this will become line once water is warm enough, so SW1 is made to grey when half way and SW2 is made when all the way, white is CH and grey NO DHW.

So for DHW on its own valve does not move and the boiler gets supply from the tank thermostat.
for DHW and CH the boiler is still powered from the tank thermostat, and the motor in the valve is powered by SW1 until half way, then the diode and 13kΩ resistor hot it in centre position.
for CH only power on the grey moves valve all the way, and white powers boiler through SW2 and orange wire, but in your case no power on grey if programmer switched to DHW off, so CH would not work, if the programmer was set DHW on then when tank warm enough it will just run CH but not is programmer turned off.

With the existing programmer on page 5 of the link given it talks about an interlock, I seem to remember there was a plastic screw driver head bit which when turned stops you selecting CH without DHW, designed clearly for C Plan but if that had been turned then it should have worked, I seem to remember making the mistake myself in Stanley village near Heathrow air port, I move the turn buckle so could select central heating without DHW not realising that the plumbing will not allow it.

 

[phmode]

Thanks for all of that and it makes sense. The interlock in the Horstmann is definitely not set, both plastic screw heads are/were vertical. I say 'were' because that is where the HW was set when she moved into the house but the CH screw head was most definitely angled slightly over counter-clockwise and that combination is not mentioned in the installation/user instructions for the programmer.

I made a point of setting the CH one to the vertical position but once the switch has been moved a couple of times it, the CH screwhead, seems to move slightly counter-clockwise of its own accord. And there is no mention of that either. The programmer is so clunky and out-dated that even if it were working perfectly I would swap it out for a 'modern' one. Either way, the Hive is going in once I have determined where all the cabling goes. Thanks again and once I have worked it all out I shall report back. Brian

 

[phmode]

Time to put this thread to bed.

Having got the lady moved into her new house, the dreaded pandemic meant no more work on this system until the restrictions were lifted.

I have since stripped out the rat's nest behind the original, defective Horstmann and replaced it with a separate patress box and chocolate block prior to eventually fitting a Lifestyle wiring centre at this end of the wiring run...



...with a second one replacing the junction box in the airing cupboard for neatness and completeness.

And as you can see, I now have the Hive receiver fitted alongside and working perfectly within the limits of the wiring...



Once all the wiring behind the Horstmann was exposed it became obvious that the 'missing' wire to terminal 3 was not a mystery, merely a system wired to operate on the basis of no CH without DHW, possibly in some earlier or even original installation. The place was converted into a dwelling back in the early '90's.

For now, the system is still working in this configuration (with the Hive schedules for CH and DHW set to run at the same times) until such time as I can get a cable through the gable end wall from the garage into the rest of the house. I could re-purpose the wire from the room stat but don't like to make things non-reversible and if Hive ever disappears then reversible it will need to be.

So, many, many thanks for all the great help and suggestions I received with this problem. Brian

 

[Johnmdc]

You could set the Hive into "gravity mode", then when heating is set to come on it will also turn the hot water on automatically.
To do this first turn the power off wait 10 seconds then turn it back on.
Now press the left hand silver button on the receiver for 10 seconds and the top green light will turn blue.
Job done.
The other alternative is to wire the receiver into the junction box where the valve is, but that would require a few wiring alterations.

 

[phmode]

Excellent idea.

If she decides to do this, can she still have hot water only?

Also, when I get around to adding the additional wire (its a 10m run through a con-block gable wall and an almost inaccessible loft space) how does she turn the Hive back to 'normal' operation? Is it just the same button presses again? Brian

 

[Johnmdc]

Yes the hot water would work in its own.
Just repeat to set back to normal operation.
If you moved the receiver to where the valve is you wouldn't need any more wires just a case of reconfiguring the existing one.

 

[phmode]

Now...why didn't I think of that That is thinking outside the box. The only thing in the garage is the boiler and the supply and putting the receiver in the airing cupboard with everything else is much more convenient for the lady owner.

I remember replacing a 40m bundle of 40'odd way cable on a Britannia aircraft at RAF Lyneham back in the late 60's. When I got someone to help check it out he said "all this cable does is go to a junction box down the back end where it gets some of the pairs shorted and that's it. You could have bypassed the entire cable by moving the junction box up to the front...". I remember thinking at the time 'two weeks work and now he tells me'. And some lessons are never learned.

Back to the drawing board! And thank you.

 

[phmode]

Well, yet another lockdown. But, before we all got sentenced, I finally managed to get everything working.

I followed John's excellent advice and moved the Hive receiver to the airing cupboard. This meant that there were enough cables to re-jig everything without having to venture into the loft to add more.

I had already bought two Lifestyle wiring centres, one for each end of the run and although that was now overkill at the boiler end, it produced a much neater and more logical result than the original...

...and as the boiler has its own froststat built in, the wiring became even easier as I could now ditch the separate one.

The result in the airing cupboard was even better...

So, all in all a great result and the lady is delighted. No need to visit the garage to set the hot water 'on' just so she can have heating 'on' and indeed no need to visit the airing cupboard because she can control everything on her Hive schedule and have whatever combination she likes, even turning her heating on before she gets home from a weekend away. Doncha just love technology? When it works.

So, many thanks to everyone for their help in getting this one over the line and especially you John, for suggesting moving the receiver. Genius, sheer genius