pump on

[fire]

my pump stays on and when i turn off the cylinder stat it switches off, thought cylinder stat was faulty so put a new one and still does the same.

i then disconnected the zone valve and its still on.

its controlled by a drayton LP722 and we have not set any demand on it (its off) when i switch the hot water on even the raditors come on.

i was all working fine till one day when the 3A fuse on the spur blew and all the above started after replacment.

any help on this please.

 

[5544]

Doh !!
Sorry 5544. You beat me to it !

well assuming it has pump over run, then the pump will stay on long enough to get the system below the required temp, normally about 5 mins. In honesty it takes some going to blow a fuse on a central heating system. Normal suspects would be the fan or the pump. the only other areas would be a failure of the elcetronics, but then, you would expect that they would not work again once re energised making it easy to detect.
if you look up the operation of a three port valve on the internet (sorry im too thick to add it to this), and find a good schematic then it becomes clearer how the system works. as previously stated, the tank state is really a simple switch and rarely goes wrong. the good thing is that fault finding on these systems is easier since you can break it down to external controls or boiler quite simply.

 

[sambotc]

My bet's on the three port valve jamming, probably the valve spindle itself causing the syncron motor to stick in the open position which is keeping the micro switch on. That would also account for the heating staying on whilst only hot water is called for. Not sure why the boiler isn't firing though, unless its clicking on and off on the stat or it has been isolated. It's unlikely that a back boiler would have pump overrun as the the heat exchanger is not low water content.

If you have 240v on C terminal at the cylinder stat whilst everything is off then the programmer is faulty so worth ruling that out first. Check both when the cylinder stat is open (calling) and closed (satisifed) to rule out back feed onto terminal C.

All of this is assuming nothing has changed recently, like a replacement 3 port which could have been fitted in reverse or a new programmer wired incorrectly.

 

[fire]

sorted, the pcb on the programmer had shorted hence keeping the pump on. does anyone know why the room stat has a neutral and the cylinder stat hasnt?

 

[sambotc]

I can't quite remember what its called but, unless you have a neon indicator on the stat which needs L+N, the neutral is used to make the stat slightly more accurate, it will work without as its only a switch but if you've got a neutral there already then bobs your uncle.

 

[sambotc]

I won't try and blag everyone into thinking i've remembered off my own back as I didn't so here it is from another site!

Anticipator / Compensator heaters

Bimetal room stats use a compensator resistor to enable them to maintain a steady temperature. This mostly cancels out the inherent hysteresis of bimetal stats. This inbuilt resistor is also known as an accelerator resistor or compensation resistor.
This resistor requires a neutral connection to work; without this connection the room temperature will swing up and down by a few degrees, which is not satisfactory.
It is possible to miswire a bimetal stat so that the compensator is on at the wrong times. If this happens a wide range between switch on and switch off temps will be seen.
Hot water stats don't require such temperature accuracy, so don't incorporate a compensation resistor and don't need a neutral connection.

 

[JD6400]

I won't try and blag everyone into thinking i've remembered off my own back as I didn't so here it is from another site!

Anticipator / Compensator heaters

Bimetal room stats use a compensator resistor to enable them to maintain a steady temperature. This mostly cancels out the inherent hysteresis of bimetal stats. This inbuilt resistor is also known as an accelerator resistor or compensation resistor.
This resistor requires a neutral connection to work; without this connection the room temperature will swing up and down by a few degrees, which is not satisfactory.
It is possible to miswire a bimetal stat so that the compensator is on at the wrong times. If this happens a wide range between switch on and switch off temps will be seen.
Hot water stats don't require such temperature accuracy, so don't incorporate a compensation resistor and don't need a neutral connection.

To be honest i already new that , but i did think that it still deserved your first " Thanks " .:smiley2:

 

[sambotc]

what can I say, i'm chuffed that someone finds me useful!

 

[JD6400]

A like as well , steady now they will be talking !

 

[sambotc]

see how you've got the crowds flocking. 2 likes now, that makes me twice as useful as I was 10 minutes ago

 

[fire]

my 3 port valve remains warm when there is no call for water or heating, is that the way it should be?

 

[sambotc]

Yes possibly depending on what position it was last at before it was de-energised, as the motor is 'stalled' with a lower voltage to prevent it returning on the spring mechanism.

 

[5544]

Synchronized motor can stay energized even when both hot water and heating are satisfied as it can still be stalled in the heating position. I would change the room stat for a new digital one which onlt need common and switched live.