Central Heating header tank overflowing

[steve-t]

I've just drained and refilled my vented oil fired central heating system after fitting a new radiator.

I've replaced the rad on the ground floor of a 2 storey house. I've use JG speedfit plastic fittings and pipe, onto the original copper system. The joints, rad and pipework is all good with no leaks and the rad works fine. The rad was old and partially cold, hence it's replacement, other than the system worked fine previously.

The system took a while to refill but is now complete after several bleeds of the other rads. The issue is that the header tank keeps overflowing, this only appears to occur when the heating is on.

I have take 12 pints of water out of the header tank and reduced the level to an inch below the overflow outlet, however the level has again risen and the tank periodically overflows. The ball cock appears to be working fine and does not activate at this water level.

I am still bleeding air out of the top rad, could it be there is still air in the system which when heated, pushes water back up into the header tank, or is there another problem?

Any ideas gratefully received.

Kind regards,

Steve

 

[jtsplumbing]

Is the header tank lower than main cold water storage tank ? you may be unlucky and have a hole in the coil inside hot water cylinder, is it pumping over through the vent pipe into EX tank ?

 

[GrahamM]

If all ok before then would say its a circulation/overheat issue and is pumping over.
Anything else altered? Pump speed, boiler temp stat turned up higher since before work done?

 

[tamz]

Water lever should be at least 3 -4" below the overflow level when its cold. Water expands when it is heated and so you need room to accommodate that. That is why its called a feed and expansion tank.

 

[wild nomad]

There is an outside chance that the new rad offers less resistance than the old one so the water is being pumped round the system quicker and is now pumping water up the vent pipe and into the feed and expansion tank. Also check that the Vent pipe is at least 450mm above the water level. Sometimes it needs to be higher if the tank is quite far from the Boiler.

You need to find out where the extra water is coming from really. When the pump is working check the F&E tank to see if water is coming out of the vent pipe. If it is then it could be over pumping. Set the pump to a lower setting. If it continues to spill out then I would check the boiler thermostat and the over-heat thermostat.

If it's not coming out of the vent pipe I would say you may have a small hole in your heat exchanger (as suggested by JTS Plumbing). Have you noticed any discolouration, smell, or unusual taste coming from your hot water taps?

Also, I know you have checked, but double check that Float operated valve again. Even a slow drip may eventually fill up the tank.

 

[steve-t]

There is an outside chance that the new rad offers less resistance than the old one so the water is being pumped round the system quicker and is now pumping water up the vent pipe and into the feed and expansion tank. Also check that the Vent pipe is at least 450mm above the water level. Sometimes it needs to be higher if the tank is quite far from the Boiler.

You need to find out where the extra water is coming from really. When the pump is working check the F&E tank to see if water is coming out of the vent pipe. If it is then it could be over pumping. Set the pump to a lower setting. If it continues to spill out then I would check the boiler thermostat and the over-heat thermostat.

If it's not coming out of the vent pipe I would say you may have a small hole in your heat exchanger (as suggested by JTS Plumbing). Have you noticed any discolouration, smell, or unusual taste coming from your hot water taps?

Also, I know you have checked, but double check that Float operated valve again. Even a slow drip may eventually fill up the tank.

Apologies to for a late reply to all of those submitted.

I do need to recheck the expansion tank, however I'm pretty confident that the system is filling this tank and over flowing as there is black radiator staining on the outside wall (the overflow goes into the roof gutter, which appears to be blocked and consequently runs down the wall)

I'm happy that the ballcock is all good because the tank would be overflowing all the time rather than when the boiler is in operation, but happy to take advice on that.

The hot water taps are good.

One point of note is that the tank overflows when only the hot water only setting is on the boiler, which would also be running at the same time as the CH.

Regards,

Steve

 

[steve-t]

It has a GRUDFOS pump fitted with 3 settings

40,65,95 P1(W)

I've changed it from 95 down to 65 and the problem appears to be cured!!

the CH system work ok still and the pump is quieter, are there any issues with reducing the flow from the pump?

The old rad was only working at 50% as there were cold spots in it, so over pumping does make sense.

I have checked the expansion tank and that is all good.

Regards,

Steve

 

[wild nomad]

It has a GRUDFOS pump fitted with 3 settings

40,65,95 P1(W)

I've changed it from 95 down to 65 and the problem appears to be cured!!

the CH system work ok still and the pump is quieter, are there any issues with reducing the flow from the pump?

The old rad was only working at 50% as there were cold spots in it, so over pumping does make sense.

I have checked the expansion tank and that is all good.

Regards,

Steve

Glad it's all sorted Steve. Looks like it was over pumping. The only issue with reducing the pump setting is that some radiators on hi resistance circuits may not get as hot, but if this is not the case then all seems well.

If you do need to turn up the pump for any reason then extending the height of the vent pipe over the F&E tank should help with the over pumping problem. Current regulations state that it should be at least 450mm above the water level. Of course, if it does happen again it could be that another rad is blocked so check for that first.

Sounds like its OK now though so 'if it ain't broke don't fix it.'

 

[steve-t]

Thanks for your advice

 

[newcastle phill]

Just wondering did you take the pump off at any point

 

[steve-t]

Just wondering did you take the pump off at any point

No, didnt remove the pump, no need.