Pump overrun

[mareng]

I have a fully pumped open vented Ideal Classic boiler. ACL Lifestyle timeswitch LP241. Landis & Gyr PID programmable room stat.
I control DHW on the ACL and CH on the Landis & Gyr (with the ACL set to 24 hours on) and run like this for last 13 years or so without problems.

After the Heating has shut down for the night on the Landis & Gyr (21.30) the pump is still running at 23.30, no call for heat or DHW.
Turn the room stat to OFF and the pump is still running.
No changes to system or wiring since boiler fitted.

Please advise.

 

[kbdiy]

Motorised valve jammed open. Do you have a 3-port or 2 x 2-port valves?

 

[mareng]

Thank you kbdiy.
I have 2 two port valves.
This is the 2nd time it has happened and I thought it was a blocked pump first time, so checked the pump, but clear.
Will try operating CH valve manually to clear blockage if that will do it.

 

[kbdiy]

I would test each motorised valve by turning the whole system off then operate each valve manually. You should normally feel resistance against the lever but if not that would suggest the faulty valve - jammed open so no resistance.

 

[mareng]

The motorised valve opens by itself when thermostat calls for heat, closes when up to temperature but pump still runs if thermostat is turned off.
Could the motor drive have sheared from the valve stem that is in the open position, yet still show the right positions on the open/close valve indicator?
Reading the Drayton valve leaflet it talks of a auxiliary switch in the valve that is not electrically connected (but may be mechanically connected)such that when the valve closes shuts off the pump.
How is my reasoning?
I am not a plumber nor an electrician but a Marine Engineer.
I have now matched my ACL HW program to my Room Stat program so hopefully the pump will go off in the evening.

Any more thoughts.

 

[kbdiy]

When the motorised valve opens a microswitch makes to send power to the pump and boiler (in most configurations). If the valve is jammed open, the microswitch remains closed and thus power is permanently connected to the pump/boiler. Hence why I suggested turning everything off and checking physical resistance using the manual lever. If the valve is open you wont feel any resistance and have therefore identified the jammed valve.

Of course there could be a number of other causes of your probelm but this one is an easy test to start with.

 

[mareng]

kbdiy.
To reply to your 2nd post, yes I think the CH valve is faulty as you don't hear the same sounds as the DHW or the slight resistance.
This will mean a whole new body I would assume with a partial drain down.
I have changed them before when I changed the boiler, so it is not a problem, just the time of year and (SWMBO).

Thanks for your help.

 

[kbdiy]

Yes unfortunately not the best time of year to have to mess with heating issues. It does sound like you may have to change the valve body but might be worth removing the motor from the body first and double-checking that it is jammed by trying to rotate the shaft by hand (grips/pliers). Make sure you isolate the electric supply first. Can be tricky if access is restricted.

Hope you get it sorted.

 

[mareng]

Thanks I will give that a go.

 

[JBPHS]

You may get away with changing the synchron motor only.

James.

 

[mareng]

Since I married the Room Stat times to the Programmer the CH valve seems to have been working ok and shutting off the pump as it should.
The overrun only seemed to happen at night and only twice.

Looking at an old 2 port valve I replaced with the present ones in 2002 the lever from the synchron motor does not touch the microswitch, in fact it is about 3/16" away when in the open position, leading me to think there was a pad on the lever or the microswitch was longer by that amount. I can see that the CH valve would wear more than the DHW as the DHW valve only moves twice a day, whereas the CH is open and closing perhaps 8 times a day.

Checking the old sychron motor, I had a high resistance so that was ok and the microswitch opened and closed electrically, though they were working when removed.

Will keep an eye on the pump for overrun during the day. Seems an intermittent problem. At least I know how everything works now.

 

[JBPHS]

This not sorted yet?

Isolate electrics. Remove the motor head. Check that spindle moves freely by hand only. If ok, check for safe electrical isolation and replace motor. If spindle is stiff replace entire valve (my preference is Honeywell). Re-instate and test.

There is no pad that sits on the micro switch, motor is struggling to make the switch, I.e. Faulty motor, high resistance on travel of spindle or both.

Simples.

James.