Honeywell ST7100 - help !

[nemo2000]

I have a Honeywell ST7100 on my CH system. Knowing that the back-up batteries had been in there for some years, I decided to check on them today - bad move :-(

I turned off the 230V supply, removed the ST7100 from its backplate, and tested the batteries - they seemed still good. Replaced the batteries, replaced the controller, turned on the power - various 'clicks', but no display :-(

Turned off the power again, removed the controller, fitted brand new batteries, and replaced controller. Display came back and most of the programming intact, just needed to set date and time. The indicator lights go on/off as expected if you press the relevant buttons to advance the programmes (accompanied by various 'clicks' which I assume are the relays working), BUT......the boiler keeps firing intermittently even when the programmes read 'OFF'. (I have had to turn the boiler thermostat to 0 to stop it!)

In short - is the programmer broken????? Do I have to replace it, and if so is there an equivalent that will fit the same backplate?

 

[JohnKay]

Hi nemo2000
Although it sounds like a dodgy programmer, this may not be the case. It's possible that you have a defect with a motorised valve, showing itself due to the power being off and on.
Could you provide a bit of info on the system, do you have motorised valves on the system ?
I would be looking at establishing that the programmer is faulty before thinking of changing it.
I'm not sure if the back plate is the same on later versions, being retired, not much contact with them now.

 

[nemo2000]

You may be right

My initial thought was that one of the relays in the programmer had fused its ON contacts and thereby 'pretending' to be ON when it was not. Testing the unit off the backplate the ON contacts were open, the OFF contacts were closed on both relays, so probably not that.

The CH relay ON position simply feeds the CH pump.

The HW relay ON position feeds thru' a cylinder stat to a Honeywell 8011 motorised valve on the gravity circuit to the HW cylinder. The switch on the valve feeds to the boiler when the valve is open (ie stat is demanding heat). Not quite sure yet where the 'live' feed to that switch originates, but it appears to be constant. When I disconnected the output from the switch, the boiler ceased to fire.

At the moment I have disconnected that switch from the constant (?) live and connected it to the ON side of the HW relay. At least now the boiler does NOT fire if neither programme is ON. The valve itself /appears/ to open/close with the stat, but difficult to tell at the moment. What would happen if the valve stayed shut, but the boiler kept firing as/when the water in it cooled down???? Maybe its time to turn the CH on and keep the water circulating?

I need to investigate the wiring at the programmer a bit further, but that needs more time tomorrow to get the back-plate off the wall and see exactly what goes where.

 

[nemo2000]

...also please...

I have been hunting for wiring diagrams for the valve, which apparently (from the model number I found hidden at the back!) is a V4043HA1106 (it said 8011 on the front). There are various example diagrams for the external connections, but none seem to match my setup, nor can I find any schematic for the actual switch.

There appears to be:
Brown and Blue for the actual motor
Grey, Orange and White for the switch.
Grey seems to be connected to a permanent live (the 'C' of the switch?)
Orange is connected to the boiler (contact closed when valve open?)
White is connected to the pump (contact closed when valve shut?)

On my system there is a valve ONLY on the gravity feed to the HW cylinder, controlled by a cylinder stat. The radiator circuit has no valve and is pumped all the time that the CH is ON - there is no room stat (TRVs everywhere!).

So - what is the point of what seems to be a system that runs the pump if the HW is ON, but the valve is shut (cylinder water hot enough), but the CH is off? Should the white wire actually be connected?

Mind you, until today it has all worked OK for y-e-a-r-s.....

 

[JohnKay]

There were some odd systems around, but as you say, it worked for years !
If you go to honeywelluk.com you should be able to find a standard diagram for the valve as used for a heating zone valve.
Your description of the valve function looks corect.
I hope you can see why I made the suggestion !

 

[nemo2000]

Indeed. I have studied all the Honeywell diagrams that I could find, but none seem to match my set-up :-( I'm still puzzled as to what to do about the white wire.....

 

[JohnKay]

What you have is a Honeywell C plan, the white goes to the pump, and is linked to the 'on' of the room stat. In the valve the orange is the common of the switch, switching to the grey when open, and to white when closed.

 

[nemo2000]

It gets curiouser......

I did some more testing today and found nothing apparently wrong with the valve auxiliary switch. Out of curiosity I re-wired it back to the original 'permanent live' and the original problem of boiler constantly firing did NOT re-occur. So heaved a sigh of relief, but as a precaution re-wired it again back onto the HW switched live just as a precaution. Ran system for a while with no problem, then turned off and got on with other tasks for the day.

Hot water program came on again about 4:30pm as programmed and everything seemed to run OK for about the next 30 mins. CH came on, but not needed, so I turned it off. About 5 mins later it was all hell let loose, with violent banging and rattling and boiler 'boiling' noises and pipework knocking etc etc, so I shut the whole system off as a safety precaution.

[ I decided to invoke the emergency cover of my insurance which covers 'CH failure', only to be told that - as I had shut it off myself - it was not a 'breakdon' and therefore not covered by my policy. Had I left it run and it had blown up and broken, then they would have dealt with it !!!! Ironically I'm in the process of trying to book a boiler service at the moment, but can't get anyone for at least two weeks <grrr>. ]

I did wonder if the motor valve on the gravity circuit was shut, but the switch still closed and therefore calling for heat? Difficult to tell what the valve is doing from outside, but it /appeared/ to be powered over to the open position. Is it possible for the actuator to operate, but the valve itself to stick?

Do the symptoms sound familiar to anyone? Is there anything else that I could try without risk of danger/damage?

 

[JohnKay]

Looks like our posts crossed as it were (bad timing)

Sounds like the valve had closed, and caused boiling. If you look up C plan you may get a better idea of the wiring.

 

[nemo2000]

My system is basically a C plan *except* that the valve is only on the gravity fed to the HW cylinder - it does not control the CH circuit. There is NO room-stat, so the CH 'ON' (terminal 5 on the programmer) is connected direct to both the boiler and the pump. The TRVs on the radiators manage the room temperature, while the boiler thermostat maintains the water temperature.

The WHITE wire from the valve switch is connected to the pump L as per the plan, but IMHO this is superfluous as it merely therefore connects the boiler L and pump L together, but they are already linked together anyway at the CH 'ON' terminal. I propose to disconnect the WHITE altogether - OK?

As posted previously, I have re-routed the switch GREY cable from the permanent L to the switched HW 'ON' L. This ensures that, even if the switch jams in the "valve open" position, the boiler won't fire if HW is not ON - OK? (It does not impact the CH-only scenario, as the boiler is always live when CH is ON).

My questions are - if the boiler is firing when the valve is shut, then (a) why does the boiler thermostat not shut it down and (b) what will happen eventually - is it dangerous?????

 

[JohnKay]

The system you describe, with a valve on the gravity hot water only is a C plan.
When HW is on the valve is powered open, and the boiler is supplied by power from the grey to the orange wire.
If the cylinder stat opens. the valve closes, and the switch connects the orange with the white, powering the pump and boiler.
It MUST be wired as in Honeywell's plan.
Have you looked up the plan, rather than the valve.
honeywelluk.com/products/Systems/Wired-Sundial-C-Plan/

If the boiler fires with the valve closed, the boiler thermostat cannot act fast enough. Although not a good situation, the system is open, with an open vent pipe terminating over the F+E tank to dissipate the pressure.

 

[nemo2000]

A further thought...

The original system had a simple gravity-fed HW cyclinder. I added the cylinder stat and motorised valve at a later date.

Suppose that I disconnect the valve from the cylinder stat and use the manual control lever to keep it open permanantly. [I would need to secure the lever somehow, as I have found in the past that it tended to work loose after a while, especially when the motor was still wired to the stat.] I would then re-wire the boiler feed either to the programmer HW ON terminal (as was the case originally), or more easily to the cylinder stat (so that it is only live on demand for heat).

Provided that the valve really does open with the lever (and no doubt that will become obvious rather quickly!), this ought to keep things going safely until such time as I can get the valve checked out and probably replaced when the system is serviced - hopefully in a couple of weeks.

Any comments, possible problems etc please????

 

[nemo2000]

Ooops - my message leap-frogged over the reply from John Kay!

John....your link did not yield a C plan, only S or Y, but I *have* looked at a C Plan in the programmer documentation. My impression of the C Plan is that the one valve controls *both* the HW and CH circuits, which is not the case on my system. With no room-stat, then it is not possible to wire *exactly* as the Plan.

>>>When HW is on the valve is powered open, and the boiler is supplied by power from the grey to the orange wire.....

Yes but...when HW is ON then the valve is powered ONLY when the HW cyclinder is cool, so the cyclinder stat closes and then powers the valve.

>>>If the cylinder stat opens the valve closes........

Agreed

>>>>and the switch connects the orange with the white, powering the pump and boiler.

Err.....it connects the boiler to the pump, but with only the HW ON it does not power anything as the power to the boiler comes from the grey, which is of course now disconnected with the valve shut. When the cylinder stat is 'open' then the boiler and pump only require power if the CH is ON as well, in which case they get it from the direct wire from the programmer CH ON terminal. That is why IMHO on the HW only situation the white does nothing and with CH on it merely duplicates an existing connection.

 

[JohnKay]

I think you are missing something here. just Google Honeywell C plan and go with the Honeywell site for a PDF of the layout you have. The fact that you have no room stat makes no difference, it's only a switch after all ! imagine a link between terminals 5 and 6, and the neutral wire removed.

Please take note of the internal switching, I think you are not seeing that the common is on the orange, switching from grey to white. grey is not the common. Just take your time to follow the live round the diagram (OK leave the room stat out) all should become clear ! The white must be connected for the system to work as intended.

The manual lever only partially opens the valve, it can be kept in that position by the latch,but will disengage if the valve is powered fully open.

 

[JohnKay]

Sorry, slight correction, I meant terminals 4 and 5, for removal of room stat.

We've done well, not often to get to a second page on this forum !