Pump running 24/7, and bypass gate valve appears closed & leaks when opened...

[perfectplanet]

Hi there

I'd really appreciate any advice regarding this problem, before I call an engineer out.

We moved into a new house last year. CH and HW all seemed to work fine. However the pump is on 24/7 - even when the room thermostat and programmer are all off. Initially the problem was intermittent, clearing itself after a few days (whereupon the normal pump overrun would work fine, shutting the boiler off after an hour or so), but now the pump just runs and runs unless I flick the main power to the boiler off.

I believe we've got a Fully Pumped Open Vented "S-Plan" system. The boiler is a Potterton Profile 60 and is in the garage, connected to a frost stat. The electronic timing programmer is a Potterton EP2001 and there is a single room thermostat (Sunvic) in the hall.

In the upstairs airing cupboard next to the HW cylinder, the Grundfoss pump feeds into two separate 2-pipe Sunvic zone valves, one each for the CH and HW. There is a bypass circuit which runs from just above the pump (& before the values) and connects to the hot water cylinder return pipe. It has a red gate valve on it which APPEARS to be fully closed. I'm not sure though, because when I try and turn the valve anticlockwise to open it, it starts leaking! Also when I turn it it feels like the tap isn't actually turning the valve inside but is instead just unscrewing itself from the valve unit (I'm 100% not sure this is the case though)

So, right now the electronic programmer is off, the room thermostat is set to low, and the pump is whirring away as usual. The boiler will fire up every now and then, burning a short while each time before switching off. The pipes above and below the pump, above both zone valves (which I think should both be closed?), and the pipes going into & out of the HW cylinder are ALL very hot. No radiator pipes are hot though.

Any ideas on what's going wrong here?

Reading about on the net it seems to me likely suspects might be:
1) One or both zone valves are faulty?
2) Some effect of the bypass gate valve being closed? (if it IS closed!)
3) Dodgy frost stat in the garage, keeping the boiler on despite the ambient temperature being high?

One additional bit of info, is that although the CH and HW do appear to work fine, I can sometimes hear a water flushing noise, which I suspect might be the HW venting into the cold water storage tank (but I haven't 100% verified this yet).

Many thanks for your help,
Simon

 

[Reg Man]

The pump should not run continously, so wiring problem. Bypass should be automatic spring loaded.

 

[perfectplanet]

Hello,

I'm not sure it's a wiring problem, as until recently the pump overrun worked correctly ie it kept the pump on for a short time after CH/HW turns off, in order to dissipate heat. It's only recently that the pump has begun to stay on 24/7.

I've taken the actuators off the spindles of the CH and the HW zone valves and verified that they are working correctly (ie rotating on/off as the programmer and thermostats require). The spindles rotate freely by hand. So they appear to work OK - unless it is possible that there is some electrical fault with them that means they are always asking the boiler for heat??

If not, then I guess I'm left with either the frost stat, or something else which is causing the pump to stay on the whole time (and the boiler to occasionally fire up with it). Any ideas?

Many thanks
Simon

 

[perfectplanet]

Just in case anybody else has this problem, I found the fault. It was basically a stuck microswitch on the CH zone valve actuator. When the valve closed the microswitch was stuck 'on' (I used a multimeter to test it), thereby incorrectly telling the boiler/pump it still wanted heat. The HW valve was fine. So I simply replaced the actuator on the CH valve with a new one. Wired it back up carefully and all works great.

 

[turnpin]

Thank you for letting us know you found and rectified the fault and what it entailed so it may help someone in the future with a similar problemregards turnpin