Central Heating Pump will not stop

AndyDIY999 · 27 Oct 2009

Hi,

First of all I'm an amateur, so please forgive if I don’t explain properly. I’ve looked on FAQ’s etc and previous posts, but can’t find an answer to my problem.

Bit of background, we have a sealed Central Heating system with an Ideal Classic Boiler and a Megaflow Hot Water tank. The system was really badly clogged up with black ‘water’, so over the summer I drained it and flushed it out thoroughly from the mains – via the feeder loop. I’ve also just replaced the feeder loop cos the valve on the old one was leaking water into the system all the time. I also added inhibitor when I refilled the system.

The problem I’ve now got is that the Central Heating Pump (separate unit just above the boiler) seems to run all the time. Even if the water is cold (several hours after switching boiler off – on the panel on the boiler) it is still running. The only way to stop it is to switch the boiler off at the wall.

I am not sure but I think this may be linked to the expansion vessel needing to be recharged? I don’t think the diaphragm is broken - no water came out whenI pushed the central pin in inlet air valve is pressed in. But almost no air came out either – so I guess its not charged..?

Any idea what could cause the pump to run all the time..?
Thanks, Andrew.

muggles · 27 Oct 2009

First of all, the pump running is not linked to the pressure in your system/expansion vessel, although you should re-charge that anyway. The pump will be wired to the controls on the boiler/programmer, if they're not turning it off it's either wired incorrectly or there's a broken switch somewhere.

Do you have a room thermostat? Does the pump still run if you turn this all the way down?

picasso · 27 Oct 2009

your right about the expansion vessel but we need the exact model of your boiler to help with the pump problem.

AndyDIY999 · 27 Oct 2009

Yes, we have a room thermostat located in the hallway, even when this is turned right down the pump still runs. I can understand the pump running for a short while after the boiler has switched off – presumably to prevent ‘hot-spots’?

Last night I turned the thermostat right down and switched the boiler off – on the boiler front panel. I got at 6am – only to find the pump still running.

The problem is intermittent – right now its OK, but I reckon it’ll start later tonight.

The boiler is an Ideal ‘Classic LXFF & FF Fan Flue Gas Boiler’ with an ‘Ideal Classic Sealed System Module FF’ fitted on top.

The pump is an external (I guess there is one in the boiler but that is not the one I’m talking about) ‘Grundfos Selectric UPS 15-50’.

Thanks for help and advice.

Tipper · 28 Oct 2009

Is there a motorised 2 or 3 port valve on the system?

If so then the motorheads can fail and either lead to sluggish response of the heating turning on or the heating/pump staying on.

Therefore you may need a new motorhead fitting to the valve as this controls the power to the boiler and pump.

picasso · 28 Oct 2009

when was you megaflo installed? I reckon whoever installed it has cocked up the wiring, there is no over run stat on your boiler and if it was a faulty 2 port valve the boiler would be running at the same time as the pump.

doitall · 28 Oct 2009

Who fitted the megaflow, and did it have the correct G3 qualifications.

AndyDIY999 · 28 Oct 2009

Hi, Thanks for tips.

Megaflow has been fitted in the house since new (house 10 yrs old, we’ve lived here for past 3yrs). No idea who fitted it. But think it's OK, cos this problem is recent.

I had to google for motorised valve, I think we have one of these (I’m an amateur). It’s a blue box attached to a special valve located in the airing cupboard. It can be easily disconnected just by squeezing in the tabs on the side. It’s got a manual over-ride control on the top? I’ve noticed that when move this control the pump stops. But as soon as I let go it moves back to the original position and the pump starts again.

How do I know if this is the faultly part?

doitall · 28 Oct 2009

The reason I ask is because there should be a Honeywell 2 port valve on the cylinder, that is wired through the thermal cut-out.

Don't touch that valve.

AndyDIY999 · 28 Oct 2009

There is a Honeywell thermosat on the front of the Megaflow, there is also (to my untrained eye) a Megaflow three-way electronically controlled valve attached to pipes next to the Megaflow tank.

The valve I was talking about in my last post is labelled ‘Valve Actuator Code BGMVSP-9’, which (from a bit of googling) is a re-branded ACL Drayton (Invensys) ZA5 Actuator.

When you say ‘Don’t touch that valve’, do you mean the Megaflow one – or the other one..?

How can I tell if the Valve Actuator Code BGMVSP-9’ is at fault..?

doitall · 28 Oct 2009

I mean the megaflow one.

Can you post a pic of the valves and pump.

picasso · 28 Oct 2009

does your megaflo look anything like this? View media item 16182

AndyDIY999 · 28 Oct 2009

Various Pics Attached:
Megaflow
Close-up of Valve near Megaflow (the one I was talking about is blue one on left hand side)
Two of the pump which is just above the boiler - which is in the utility room.

View media item 16183 View media item 16184 View media item 16185 View media item 16186
Try again - this time with the pictures - doh.

diyhornet · 8 May 2011

I have a similar problem, what was the solution?

mysteryman · 8 May 2011

It sounds like a faulty pump overrun thermostat in the boiler. A constantly running pump is not the pump's fault!

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Central Heating Pump will not stop

mysteryman

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