Even though the programmer auto time setting for hot water is off, the boiler fires up. (The Heating is permanently off currently.) Why should this happen? Is there a problem with the hot water zone valve? Is the tank thermostat faulty? The water does seem to get hotter than the 50C setting. The boiler is a Potterton Netaheat MK 11F 16-22 and is 20+ years old. The zone valves are Danfoss HPA2 Series, and the tank stat is a Honeywell L641A. Can anyone offer advice?
Boiler fires up even when programmer is not on.
- Thread starter PhilipaB
- Start date
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I installed it, and rewired it again about two/three years ago. This fault has happened before but it has not been a continuous issue. I have only noticed it twice, that is two periods of time, in the 20 years it has been installed. Over the years the programmer, zone valve tops, and room and tank stats have been change, when they either failed or leaked. I have checked and double checked the wiring and all seems OK.
if the programmer is not calling for hw then your cyl stat, mot valve shouldn't be getting live power.
so i would say your programmer is calling for hw when you think its off.
or you need to check when it happens to see if the programmer hw calling is live when this happens, so then giving power to stat, mot valve, boiler/pump.
so i would say your programmer is calling for hw when you think its off.
or you need to check when it happens to see if the programmer hw calling is live when this happens, so then giving power to stat, mot valve, boiler/pump.
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If the programmer is doing that the light would be on and the on/off timing periods would show in the display. According to the time display and the absense of the on light, the programmer shouldn't be working, but the boiler fires and the zone valve (Spring return) appears closed, so presumably there is no demand from the stat. It would appear that if both zone valves are closed, both stats are not requesting heat. The boiler only runs for a short time, presumably only heating the water within the boiler and adjacent pipes. Maybe the faults in the boiler?
well now you give us the info.
has the boiler got a pump over run ? maybe a fault with that.
has the boiler got a pump over run ? maybe a fault with that.
Yes. However the boiler fires up long after the programmer has shut down, and can do it on and off many times before I end up turning the boiler off. It doesn't however do it every time. The fault is very intermitent.
I'm not sure what an endswitch is. Where is that located?
I'm not sure what an endswitch is. Where is that located?
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in one of the valves. those danfoss things are pretty common for doing that. next time it does it test the orange wires from the valves. if there is 240v there split them and see which one it is.
the boiler will get up to temp quickly and depending on your bypass may not come back on for a long time.
Probably due to a HW zone valve stuck open.
Here is the wiring diagram for an S plan. The auxiliary switch in the zone valve, which closes when the valve opens and supplies power to the boiler, has a permanent 230v supply from terminal 1. So, if the valve is stuck open and the switch closed, the boiler will fire, irrespective of whether the timer is on or off.
I have never understood why S-Plans are wired in this way - unless this is seen as a means of warning that the valve/switch is stuck!. I think it is better to wire the HW zone valve grey to the HW ON terminal of the timer and similarly for the CH grey wire.
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Here is the wiring diagram for an S plan. The auxiliary switch in the zone valve, which closes when the valve opens and supplies power to the boiler, has a permanent 230v supply from terminal 1. So, if the valve is stuck open and the switch closed, the boiler will fire, irrespective of whether the timer is on or off.
I have never understood why S-Plans are wired in this way - unless this is seen as a means of warning that the valve/switch is stuck!. I think it is better to wire the HW zone valve grey to the HW ON terminal of the timer and similarly for the CH grey wire.
View media item 72
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thats how you get backfeed in certain systems to the synchron meaning one will not close once both valves are energised even if the clock tries to shut it down.
its done that way for a good reason and the faults that you get from microswitches are not really much trouble.
That's interesting. Can you explain a bit more?
N
namsag
I would say the reason for the boiler not to fire till the microswitch is made is that way under normal operation it would confirm the valve is actually open.
If the boiler fired on same feed of power to the valve, if the valve motor failed which is more likely than microswitch failing then you have boiler firing on full pelt with if your lucky only the bypass for the heat to go round.
Back to op providing everything is wired correctlly then you have a faulty microswitch in one of the valves and it does notmatter that it is turned off at room stat and programmer, microswitch still has a permenant live to it and if it is stuck will allow power through to pump and boiler.
Or HW valve is jammed fully open which would be easily noticed
If the boiler fired on same feed of power to the valve, if the valve motor failed which is more likely than microswitch failing then you have boiler firing on full pelt with if your lucky only the bypass for the heat to go round.
Back to op providing everything is wired correctlly then you have a faulty microswitch in one of the valves and it does notmatter that it is turned off at room stat and programmer, microswitch still has a permenant live to it and if it is stuck will allow power through to pump and boiler.
Or HW valve is jammed fully open which would be easily noticed
I was not suggesting that the microswitch should be bypassed.
But with the standard arrangement (see pic below), where the feed to the microswitch is taken from terminal 1, one side of the switch (grey wire) is permanently live. So, if the switch gets stuck closed, there will be a supply to the boiler from terminal 1, no matter if the timer is turned on or off or if the valve is open or closed.
By connecting the grey wire for the HW valve switch to terminal 6 and the grey wire for the CH valve switch to terminal 4, the grey wire will only be live when the relevant timer is switched on; i.e if HW is off at the timer, the HW grey wire will be dead so the boiler cannot run through the HW microswitch.
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