Grundfos circulation pump wont switch off

[quaywee]

~just edited my post title to be more accurate~

Hi All

I've read through the various posts but am still stuck s hoping someone might be able to help.

We have an old Maxol Microturbo 40H boiler (c. 18 years old) and a Megaflo hot water tank. We've only been in the flat six months and all was fine until a week ago when I went to put the GCH on - when it came time for it to turn off, the boiler kept running (since initial post I have found out it is the circulation pump, not boiler!). It wasn't firing, but it sounded a bit like a fan running inside and I've taken to turning the elec switch on and off at the wall otherwise it would run all day.

I've unscrewed the white coverings of the Danfoss HPA2 valves following posts on here, and used a pair of pliers to move both spindles back and forth to ensure they were loose. The one that looks like it's going into the hot water tank was fine but the one which I think is for the GCH was a bit stiff and covered in green build up, which I assume is limescale. However it's loosened up now and I'm able to move both with my fingers.

I screwed the covers back down and moved the levers back and forth - both would automatically revert to the "auto" position after I moved them to "manual". I am unsure if that means the motors are working........ but either way the pump STILL won't shut off.

I'm hoping we can delay having to replace the boiler for at least a few more months as I nearly keeled over when I got a quote earlier in the week.

 

[quaywee]

Just had a friend look at it and he tells me it is actually the circulator pump that won't shut off - not the boiler.

He suggests changing the Danfoss valves in case the microswitches have blown.

Does anyone know if that sounds feasible?

Thanks !

 

[Agile]

Its very likely to be the switches in the motor valves jammed.

But with all technology the part need to be tested BEFORE blindly changing anything!

Tonby

 

[quaywee]

Thanks for reply.

Can you advise how I can test? Already paid for plumber to come round who didn't diagnose issue so I'm loathe to fork out again.

Thx

 

[quaywee]

A bit more info to add to my problem.

Earlier in the year, the heating would continue to run even when we'd switched the heating part of the programmer (Danfoss CP15) to "off" and turned the thermostat in the lounge down as far as it could go. If the hot water would come on, so would the heating. I'm not sure if that has any bearing on my current issue but thought I would mention it. I ended up just turning all of the radiators off and then forgot about it.

Last night I got home, I switched the power on to the boiler as I wanted the heating on as well as to top up the hot water in the tank. The boiler and pump both started up as expected. However, by the time I went to bed (which was after the boiler program was scheulded to finish) the pump had actually turned off! It was the first time in about 10 days that the pump had turned itself off when it was supposed to.

Alas this morning the pump came on and continued to run.... and run... and run, until I switched the power off at the wall.

 

[D_Hailsham]

It's probably the pump overrun thermostat, which is located in the boiler.

The overrun stat is supposed to keep the pump running for a few minutes, after the boiler goes off, so the boiler cools down to a safe temperature. It is obviously sticking on.

 

[quaywee]

Thanks for the reply.

Would that be the same as the "over heat thermostat"? (I can't find reference to an overrun in the manual)

 

[D_Hailsham]

Would that be the same as the "over heat thermostat"? (I can't find reference to an overrun in the manual)

I may be wrong as am looking at the manual for the Maxol Microturbo 50.

It's on the wiring diagram: left hand side, just below the overheat stat.

If there is an overrun stat, the pump will be wired to the boiler (possibly via a junction box).

 

[quaywee]

Doesn't look like we have one - in the wiring diagram there is nothing below the overheat stat.

I have "high limit stat" to the right and thermostat to the left, but nothing below.

 

[D_Hailsham]

Can you post a pic of the wiring centre (large junction box) with the lid off, so we can see how everything is wired up?

 

[quaywee]

Apologies if this is a daft question - but is the junction box separate to the boiler itself? There is a separate white box with wires coming out of it which says Danfoss WB12.

Aside from that the only things I can see in the airing cupboard are:

Boiler
Megaflo tank
Danfoss CP15 programmer
Grundfos pump
2x Danfoss HA2 actuators

If the white box is the junction I think will need to wait until Saturday (next time I am home in daylight) as the front of it says to disconnect the power supply before removing the cover.

Thanks for your help so far !

 

[D_Hailsham]

There is a separate white box with wires coming out of it which says Danfoss WB12.

Aside from that the only things I can see in the airing cupboard are:

Boiler
Megaflo tank
Danfoss CP15 programmer
Grundfos pump
2x Danfoss HA2 actuators

That's the box I was talking about.

When you post the pic, it would help if you said what each cable connects to, e.g pump, programmer, etc.

 

[quaywee]

Okey dokey, will report back on Saturday with pictures and comments as requested.

 

[quaywee]

Just wanted to let you know that we swapped the actuator and that was definitely the problem! Pump now turning on and off as it is supposed to. What a relief.

 

[Norcon]

Danfoss mv's are guaranteed to fail.

They must make a fortune on replacements.