CH System pumping over

[ziggy]

Hi Folks,

Have a fairly old open CH system with header tank in loft, hot water tank in bathroom and conventional boiler in the kitchen. Have always had problems with system "pumping over" when pump on number 3 setting i.e. continual water trickling from overflow pipe back into header tank in loft. Had 3 fairly new panel radiators pinhole and the water in the system despite having inhibitor always ends up dark-brown to almost black.

Had plumber out a few months back who checked height of header tank in relation to pump and also checked that overflow was behind the pump and all was in spec. Whilst replacing the 3 pinholed radiators, I drained whole system, removed every radiator and capped off every flow and return pipe tail apart from last on the system downstairs, and then flushed separately both the flow and return pipework with mains pressure cold water until completely clear. I also flushed every radiator I was keeping (tapping with rubber mallet to loosen any debris/sludge) and finally also used a wet/dry vacuum to suck any remaining brown water from the bottom flow/return pipework.

I then re-fitted all radiators with brand new TRV's & lockshields on every one. Having re-filled and got most of the air out and roughly balanced the system, the system still pumps over when the pump is on number 3, and when the pump is on number 2 it hardly pushes any heat around the system with radiators only getting warm even with boiler on full heat (there are 9 single panel, single convector radiators in total).

All thermostats are working (have tested them) and 3-way valve is also working.

Does anyone have any ideas what could be causing this? Is it the case that because it is an open system I can never have the pump on 3?

I'm tearing my hair out, so any suggestions would be very welcome.

Regards

ziggy

 

[tamz]

You need to change the way the system is piped ie layout of pump feed and vent. Any decent plumber will know how it is done to cure it.

 

[cdodds2004]

either alter they layout as tamz said or as a quick fix exstend the height of your vent pipe

 

[smillsey]

Im pretty young and can grasp the open vent system,

I dont know why some plumbers cannot grasp it. Its the most ingeniously simple system out there. I think they are great, other than freezing the expansion and exploding ofcoarse...

Oh and when chaps fit the pump the wrong way round 😉

Ziggy:

Check the F+E pipes are between the boiler and pump, and pump "drags" the water past the F+E pipes,

Yours looks like it is "pushing" it past the F+E pipes, raising the pressure in that region, as the rest of the heating system is a restriction.....

Causing it to overflow.

Does that make any sense?

 

[kimbo]

Is the return to the boiler hotter than the radiators when the system has been on for a while. First of all it is very rare on an unvented system to have the pump on 3 as it can pump over. With a sealed system it can be on three. If the return to the boiler is hotter than the rads it could be that the by pass which is a pipe that runs from after the pump and before the 3 port valve and linked to the return with a gate valve or similar between is opened too much, the water will take the easiest route back to the boiler. Put the pump on two and close the valve on the by pass and then open it a fraction or close it fully just to test the radiators.

 

[SafeGasInstall]

much easy is to fit a auto bypass -screw fix price £30.00
on e bay £10.00 for a Honeywell

 

[ziggy]

Thanks all, will check out some of those things you have mentioned.

 

[ziggy]

Hi,

Apologies for not getting back sooner ... not been too well.

It was the gate valve on the bypass as I had replaced it and it was fully open!

I currently have it open only half a turn and all is good with pump on number 2 i.e. all radiators working well.

Is half a turn too little i.e. is there a risk of too much pressure building up?

Also, is this the position where an automatic bypass valve would be placed i.e. as a replacement to the gate valve?

If so, for an open vented system like mine, what would be the bar pressure rating needed on the auto-bypass?

Thanx

Ziggy

Is the return to the boiler hotter than the radiators when the system has been on for a while. First of all it is very rare on an unvented system to have the pump on 3 as it can pump over. With a sealed system it can be on three. If the return to the boiler is hotter than the rads it could be that the by pass which is a pipe that runs from after the pump and before the 3 port valve and linked to the return with a gate valve or similar between is opened too much, the water will take the easiest route back to the boiler. Put the pump on two and close the valve on the by pass and then open it a fraction or close it fully just to test the radiators.

 

[ecowarm]

The auto by-pass can be fitted were the gate valve is, but if you leave the gate in, then 1/2 turn will be fine

 

[scousesnail]

Hi I know this is an old thread but my daughter is having the same problem of pumping over on a vented system but does not have a gate valve between the pump and the Sunvic 3 port valve (which I think is broken).
A plumber looked at it last week and has suggested a new boiler, a bit drastic at first new pump fitted last March and system fluched July before she bought the house which to me points to some earlier problems.
Any suggestions welocme
thanks
Mike

Is the return to the boiler hotter than the radiators when the system has been on for a while. First of all it is very rare on an unvented system to have the pump on 3 as it can pump over. With a sealed system it can be on three. If the return to the boiler is hotter than the rads it could be that the by pass which is a pipe that runs from after the pump and before the 3 port valve and linked to the return with a gate valve or similar between is opened too much, the water will take the easiest route back to the boiler. Put the pump on two and close the valve on the by pass and then open it a fraction or close it fully just to test the radiators.

 

[hammers4spanner]

did he say why you need a new boiler?

 

[scousesnail]

Yes he thought the heat exchanger could be faulty but when I asked about the motorised valve he did say that could be faulty as it is buzzing and is very hot to touch even when heating is off

did he say why you need a new boiler?

 

[tamz]

The guy who fitted the new pump has most likely caused the problem and this one is not much brighter. Check the pump speed and set it as low as you can.

 

[scousesnail]

Pump was set on lowest speed setting but pumping over quite a lot I have it on second speed now and closed down the gate valve on the CH side after the 3 port valve to half a turn which has reduce the flow into the header tank.

the CH comes on when only hot water selected from the control but does not produce hot water (I think this is faulty motor valve that causes this???)

why do you think who fitted the pump is at fault (previous owner had Brit Gas fit it) and as less than 12mths could I claim on warranty???

The guy who fitted the new pump has most likely caused the problem and this one is not much brighter. Check the pump speed and set it as low as you can.