Circulating pump runs with all 3 zones off

Rusky rusky

Hi all, I'm looking for an advice to tackle the following problem. We have a 20yo house with original 3 zone heating/hot water setup comprises 2 wired wall thermostats, wired cylinder thermostat, pump, heat only boiler, 3 zone timer, 3 actuated valves. About a year ago we have noticed that pump and boiler were heating up water circuit independently of the digital timer. The problem was intermittent and was blamed on the old Potterton prima 50l boiler which had know issues with faulty pcbs. The whole boiler system had to be turned off at the isolating switch to stop it from running. This summer we have replaced the boiler with baxi 600, new tucson pump and swapped the timer from horstmann to wiser hub (like for like replacement with zones wired to suit the new plate, existing wall thermostats were set to max temp). The problem with pump running off hours have manifested itself yet again last week. Again we traced it to the water zone as none of the radiators were coming on (all zones off on wiser app). Last weekend we have swapped the original imit cylinder thermostat for a new flomasta one - no result. In the meantime we also found a lot rust under the actuated valve (Myson MPE222) on the hot water circuit and that the valve is clearly passing water even in the fully closed position (hot water instantly passes through the valve).

Despite the sad condition the actuator closes and opens the valve when zone is switched off/on via the app. I guess my question is - what triggers the pump in this situation (boiler comes one for a brief moment and stops while pump is still running)? It happens even if I remove the wiser hub from the wiring plate and turn the isolator switch on. I dont know enough about the domestic circulating pumps but could it be deadheaded if i close the hand valve on the outlet from the cylinder coil? Is it lack of resistance in the loop what causing pump to run (again im not sure what is the sequence of signals within the system when I turn on the hot water in the app, maybe someone can explain;) The next step is to replace the actuator valve, hopefully a pipe freeze kit would he sufficient for a quick swap. I would greatly appreciate if some could bounce a few ideas of me before I start looking for a plumber/electrician to solve this really annoying mystery.

Wearb

If wired correctly (as a S plan) the sequence should be >programmer calls for heat and sends power to thermostat, if heat needed (thermostat closed) power is sent to zone valve. This power opens the valve and closes the valve end switch, sending power to the pump and boiler.

At least that's how it works with oil boilers when wired correctly. There might be some differences with gas, but I expect that it's basically the same.

So in your case the boiler and pump should only be getting power through an end switch...or possibly pump over-run or frost stat. Isolating the end switches would be my first part of the diagnostics.

Rusky rusky

https://www.boards.ie/discussion/comment/119964097#Comment_119964097

Thanks. I presume that end switches are in hub (the hub clicks when the zone is on, sending power to the right zone? I'm not sure whether the l pump overrun was wired as baxi boilers designed without the need for pump overrun.

10-10-20

And bear in mind that not all actuator valves might be fully wired back to the boiler - my hotpress one only receives power to open, but the contacts are ignored (not ideal, but not my design). So trace the 5-core from the actuator back to the junction box and check.

Wearb

End switches are part of the zone valve. Might be orange and grey coloured wires from it going back to the wiring center.

Rusky rusky

https://www.boards.ie/discussion/comment/119964144#Comment_119964144

Ok, ill need to have a look. My "wiring centre" is a junction box with a big wad of connected wires. I don't think anything is marked and the guy who was replacing the boiler said "nope, not touching that".

10-10-20

https://www.boards.ie/discussion/comment/119964161#Comment_119964161

therein lies your problem. 😂 (probably)

Rusky rusky

https://www.boards.ie/discussion/comment/119964167#Comment_119964167

I know! I’m trying to find a low hanging fruit before I invite my F-I-L with multimeter and start the “elimination” process. The thing is I don’t know why the problem is intermittent and what is the trigger.