Heatmiser neoStat wifi boiler always firing

[DetlefSchmitz]

I think that there is a way, something like 'To turn the neoStat off completely, scroll to the Power Icon and hold
the Tick key for approximately 4 seconds until the display goes blank'

 

[GeoffreyGodwin]

ok - did that on both neostats and still firing.

 

[DetlefSchmitz]

To my mind that shouldn't be happening. I have been embarrassed in the past by making assumptions, so I would be inclined to contact the heatmiser technical help line and ask if the switch between A1 and A2 can possibly be closed with the neostat switched off.

For the record I have a brand new 230V neostat here and the switch is off with no power connected.

 

[DetlefSchmitz]

One more obvious statement - I am assuming that you didn't miswire the stat the first time and weld the contacts together.

 

[GeoffreyGodwin]

I don't think so. The fact that replacing with the Slimline resolves the issue suggests it is something to do with the way the neoStats are interacting with the rest of the system. Even though the wiring should be exactly the same according to the manual.

I also noticed that when A2 is disconnected from the downstairs stat the UFH pump also disengages even whilst the system is powered.

It's almost like it is expecting a signal to stop calling for heat, even though it doesn't need this with the Slimline.

 

[DetlefSchmitz]

The way that the neostats are interacting with the system, as I said earlier, is that they are connecting A1 and A2. They should not be. The only two possibilities are;
- there is an obscure function that turns this switch on even when the flame is not displayed
- the relay contacts have been fused

Another question is that I assume these stats are connected to a heatmiser control box. I presume that the led/neon associated with this stat is illuminated. Even when the stat is turned off.

 

[GeoffreyGodwin]

The way that the neostats are interacting with the system, as I said earlier, is that they are connecting A1 and A2. They should not be. The only two possibilities are;
- there is an obscure function that turns this switch on even when the flame is not displayed
- the relay contacts have been fused

Another question is that I assume these stats are connected to a heatmiser control box. I presume that the led/neon associated with this stat is illuminated. Even when the stat is turned off.

Presumably I could rule out the relay contacts being fused (which would have to have happened on both) by disconnecting the entire unit and running a continuity test on A1 and A2?

There is no heatmiser control box for the neoStat Wifi. They are meant to run independently.

 

[DetlefSchmitz]

Presumably I could rule out the relay contacts being fused (which would have to have happened on both) by disconnecting the entire unit and running a continuity test on A1 and A2?

Exactly that. Preferably with a multimeter, but a battery and bulb would do.

There is no heatmiser control box for the neoStat Wifi. They are meant to run independently.

OK - thanks.

 

[GeoffreyGodwin]

I've just done the continuity test and unfortunately A1 links to A2 even when everything else is unplugged. I suppose this makes sense because it did seem to work for the first few minutes I tried it including turning off, which suggests they fused over a few minutes of operation.

What I am still confused about is:

- How this happened on both units
- Why is hasn't happened on my Slimline, which is now back on the downstairs wall and operating fine.

Is it possible to fix?

 

[RandomGrinch]

Is it possible to fix?

Give the neostat a couple of light taps on the back with a screwdriver handle - it's sometimes enough to loosen a sticky relay - but even if that works, it may only be a temporary fix.

 

[GeoffreyGodwin]

I'll give that a try but I won't be able to until next week.

I have disassembled and this seems to be the offending part, an HF46F relay (the slimline uses a HF49F).

There's no visible signs of damage. I could try replacing the relay but I would need to be very accurate with the desolder/solder and I suspect the same thing wouldn't happen again.

 

[DetlefSchmitz]

I have disassembled and this seems to be the offending part, an HF46F relay

I just did the same. The HF46F is rated at 3A ac, when it has a non-resistive load. I suppose the next question would be 'What load is this relay driving?' It would seem pretty certain that it is more than it's supposed to be as two of them have failed. You probably need to establish exactly what the load(s) is/are.

Also just found this: https://community.screwfix.com/threads/heating-programmer-relay-challenge.250398/

 

[GeoffreyGodwin]

Give the neostat a couple of light taps on the back with a screwdriver handle - it's sometimes enough to loosen a sticky relay - but even if that works, it may only be a temporary fix.

I've just given this a quick try having had a bit more time before I set off with the neoStat upstairs (downstairs is back to Slimline). It now seems to work as intended, whether that was due to the taps or not I do not know.

Very bizarre behaviour. How long it will stay like this is anyone's guess.

 

[Adam_151]

It seems that the neoStats are opperating standard 2 port valves, one for each storey? While they are probably designed with a UFH manifold in mind, driving a wax motor actuator or two each, Given that the screwfix link reports back that some kind of self balancing actuator (not entirely sure what one of those is) can cause the relay to stick, then I expect a three port valve probably could, and its probably not a configuration they tested at design stage when they decided to use a very small relay for it.

I think I'd be sticking an enclosure with two DIN rail mount relays next to that wiring centre to switch the valve motors..... you shouldn't have to but short of trying to shoe horn a bigger relay onto the PCB of the neo stat or sending it back as not fit for purpose its a way to try and work around the issues with it

 

[GeoffreyGodwin]

It seems that the neoStats are opperating standard 2 port valves, one for each storey? While they are probably designed with a UFH manifold in mind, driving a wax motor actuator or two each, Given that the screwfix link reports back that some kind of self balancing actuator (not entirely sure what one of those is) can cause the relay to stick, then I expect a three port valve probably could, and its probably not a configuration they tested at design stage when they decided to use a very small relay for it.

I think I'd be sticking an enclosure with two DIN rail mount relays next to that wiring centre to switch the valve motors..... you shouldn't have to but short of trying to shoe horn a bigger relay onto the PCB of the neo stat or sending it back as not fit for purpose its a way to try and work around the issues with it

Yes I think the left valve is upstairs (radiators) and right valve is for the downstairs (ufh).