Turning the Heating off stops the CH Pump

[chaffordred]

Hi, Just wondering if someone could help me with a possible CH wiring issue I have. The problem is the CH pump turns OFF when the Heating is turned OFF even if the the Hot Water is turned ON.

When both the HTG and HW are on the pump runs fine and the boiler runs fine.

When I turn the HTG OFF (and HW on) the CH pump stops. This causes the boiler to run, but turns the pump off and makes the system pressurise? because there is no flow.

It means I have to have the HTG ON (with rad valves closed) even during the summer just to keep the pump running.

I am 99% sure it is an wiring issue as I am sure the symptoms started when either the 3 way valve or the pump was changed and just to confirm it is something to do with the wiring to the pump I temporarily connected the pump to a permanent live and everything works fine fine - No back pressuring and no clanging from the boiler.

I have checked the wiring and compared with diagrams online and everything looks ok, but I feel like I am going around in circles and the problem is just staring me in the face.

The pump is in the airing cupboard and the pump live is connected to two wires (Blue with red sheath and a red wire). The blue wire is live and when I disconnect the red wire I get no heating, but the boiler still fires up and I get Hot water.

This has been going on for some time and to "get around" I've just had the HTG ON to keep the system going. Obviously not ideal, but it does the job.

Any help or pointers would be greatly appreciated as I am now at my wits end and its completely doing my head in.

Thanks.

 

[twgas]

Can you do any electrical testing, do you have a multimeter?

 

[chaffordred]

Hi, Thanks for your reply.

Yes, I have a multimeter.

 

[twgas]

What system/boiler/controls do you have?

 

[chaffordred]

Gravity Fed/Ideal Elan 2 Boiler/Danfoss controls. Thanks.

 

[twgas]

When you have HW only selected, cyl stat up (calling for heat) is there 240v(ish) to pump L terminal?

 

[45yearsagasman]

It won't be gravity fed with an Ideal Elan. Fully pumped is the correct description and you will have a zone valve of some type probably in the airing cupboard.

 

[twgas]

It won't be gravity fed with an Ideal Elan.

think he means open (filled by gravity rather than mains)

 

[chaffordred]

Apologies. Yes, I mean open (fed by gravity).

 

[chaffordred]

When you have HW only selected, cyl stat up (calling for heat) is there 240v(ish) to pump L terminal?

Just checked. HW only selected. Cylinder Stat up = The Pump is Live.

It's when the HTG is OFF and the HW is on the pump turns off the problems start.

Thanks.

 

[chaffordred]

Another symptom of this issue is the boiler is constantly on and off when there is a call for heat, so it takes ages for the rads to heat up.

When the HW is calling the boiler stays on continuously (as it should do)

Bizzare.

 

[twgas]

When you have HW only selected, cyl stat up (calling for heat) is there 240v(ish) to pump L terminal?

Just checked. HW only selected. Cylinder Stat up = The Pump is Live.

Thanks.

Is the pump working?

You say when Hw on the boiler runs continuously but the pump stops, in this scenario the boiler would, within a few moments of turning on, sound like its going to blow up

 

[chaffordred]

When you have HW only selected, cyl stat up (calling for heat) is there 240v(ish) to pump L terminal?

Just checked. HW only selected. Cylinder Stat up = The Pump is Live.

Thanks.

Is the pump working?

You say when Hw on the boiler runs continuously but the pump stops, in this scenario the boiler would, within a few moments of turning on, sound like its going to blow up

Yes, that is correct. When there is call for HW the boiler stays on. It's only when I turn the Heating off at the programmer the pump stops and the boiler continues to run and yes it sounds like the boiler is about to blow up because the boiler is producing hot water, but there is no circulation because the pump is off.

To recap:

HTG ON + HW on = All fine (Boiler and pump run OK)

HTG ON + HW OFF = All Fine (Boiler and Pump run OK)

HTG OFF + HW ON = Pump turns OFF and boiler stays on (as there is a call for HW)

Thanks.

 

[twgas]

Does the pump stop running or is the problem you have no (poor) circulation?
When you have HW only selected.

 

[jackthom]

Can you post some pictures of the inside of the wiring centre?

This is an unusual fault because generally the pump is electrically connected to the same voltage that fires up the boiler. (Either directly in parallel in the wiring box, or via the boiler PCB)

As this started after replacing the 3 port valve there's almost certainly a wiring error.