System pumping over after Trv and sys balance

[scoobydo123]

System unknown due to only just purchased house so not sure if it has always had a problem. Have flushed it (x800), removed crushed pipe on cold water feed, replaced leaky lock shields, fitted TRV's on all but one rad (where the thermostat is) flushed rads in garden with hosepipe and rubber hammer, fitted auto air vent on cylinder and balanced the system.

Before taking on all this, the system would pump over on anything other than setting 1. It now does it on setting 1 as well now! Have no magnetic attraction where the cold water feed joins the system (appears to be on the 15mm return to the closet radiator to the loft), and circulation seems good for all radiators. I would imagine I have made the system worse by balancing perhaps. Would really like to get the system working fully balanced so dont really want to wind lock shields fully open.

Was thinking of raising loop of the vent pipe above the F&E tank up to the top of the roof. If this doesn't work then also raise the F&E (could this have a positive effect?) lastly change the pump to be on the flow from the boiler rather than on the return. System is gravity HW pumped CH on a potterton kingfisher 2. The pumping over is a constant stream rather than the odd spurt (fill a litre in around 20 seconds).

Any help really appreciated.


Thanks

 

[seco services]

you say the cold feed is on the rad return before the pump ?
its poss it's taking the water down the cold feed from the f/e where you have fitted trv's and up the gravity hw to the vent.

bet hw on its own is fine ?

 

[scoobydo123]

Boiler is on the Gnd flr with the cylinder in a cupboard about 40cm above. Cold feed tee's into the radiator in the front bedroom 15mm pipe. Haven't seen any venting when on DHW only.

The system was pumping over before TRV and system balancing on anything other than speed 1 on the pump.

Trying to picture what you have said about it going up the gravity side of the HW.


Would you say my course of actions are the best way forward? IS it normal to have the pump on the return is this contributing to my issues. Real shame as the system seems to be ok apart from this.

 

[sloppytom]

Where does the vent pipe to the f&e tank tee onto the system

 

[scoobydo123]

Not 100% sure where the vent tees in. I can see from the cupboard in the kitchen a box I have opened this to find 4 x 22mm pipes so I assume 2 are flow & return 1 is hot water draw off the other I dont know. Can the cylinder vent share the vent for the F&E?

Will be going round there today so can have a good look to try and work it out. What are you looking for around this area.


cheers

 

[DP]

Scooby, radiators are balanced to achieve designated flow of water to each radiator. Large radiators need more water, small less, further away ones need less resistance (lockshield opened more) to water flow and rads close to pump need additional resistance to flow of water else water flow through these will be more than what is needed thus depriving rads on long line of sufficient flow of water.

Pump-over is due to (in most cases) faulty plumbing runs. Prefered method is boiler flow to first tee / vent pipe, followed by second tee for feed/ expansion pipe (within 150mm). Now comes the pump and then the motorised valves. While this setup can also pump over under certain circumstances, but usually pump over is caused by the header tank 'plumbed' as a radiator, so is getting flow of hot water (at the vent) and returning to boiler (via feed/ expansion pipe).

Draw a diagram of pipe runs. Mark pump outlet with + sign and pump inlet with - sign. Now visualise this differential pressure at different points in the system.

Have seen replies by various such as 1) raise the vent pipe, 2) slow the pump speed 3) 'vent should be 450 high minimum' when the vent is higher than that. 4) system need balancing. A correctly plumbed installation will not pump over with pump set to max. Equally a similar installation badly configured will pump over at minimum pump setting.

 

[scoobydo123]

Cant really re plumb without major upheval. Need to assume at some stage the system was ok. When I got the house on the 21st of december boiler was working albeit cytrol valve was jammed and had air lock in the cylinder. Pump was set to 1 and was not pumping over. Have undertook all the above preventive measures and the balancing. Was hoping to get a bit more life out of it without major cost. Was hoping for a band aid solution appreciate that pipework might not be ideal but it is what it is, is going to be difficult to find all the runs as all floor coverings are down etc.


Cheers

 

[scoobydo123]

Extended vent 2m above f&e and now no pumping over on 1 on 2 I get the odd drip. Would ideally like to get it working on 2 to get flow and return to the correct differential. Do you think raising the f&e up to where the vent is now would help?
Tks

 

[mickyg]

System is gravity HW

Not 100% sure where the vent tees in

this is what worries me most. Your vent should tee in to the highest pipe to the coil on the hot water tank, if it dosent i suggest getting it sorted. while your at it the cfeed can be plumbed into the correct position on the return from the coil. The current setup sounds like a disaster

 

[DP]

Extended vent 2m above f&e

This is not the remedy. What do you think will happen when TRVs start closing? Pump will still be pumping at the same speed remember. If the system is balanced correctly, why do you need pump to be at speed 3?

Chances are system appears to be gravity HW, but might be fully pumped. Does the pump run during HW only demand?

 

[OLLIE20]

Could always combine vent and feed, will stop pumping over for sure, wont tell you why it was doing it though, depends how bothered you are

 

[scoobydo123]

DP system is 100% gravity. Currently at first speed the circulation is not quite "quick" enough to achieve the correct flow return differential. So no the pump does not run on DHW only.

Micky G are you saying that the cold water feed should go to the cylinder as should the expansion pipe. If so this is on the gnd floor and will create major upheval. By disaster is it a safey issue in its current config.

Ollie how do I go about cominbing the vent and feed?

As before I am happy with the performance of the system, heats up quickly and is quiet. But am concerned about corrision but now it is not pumping over hopefully not an issue.

 

[OLLIE20]

You take the cold feed off the bottom of your feed + expansion tank and change it to 22mm, get rid of you open vent.

Then it cant pump over as there is no way it can circulate through the F+e tank

Although you do have to have some sort of o/ht cut out on the boiler to do it

It might not be possible on your boiler???????

 

[mickyg]

Micky G are you saying that the cold water feed should go to the cylinder as should the expansion pipe

yes thats the proper way of plumbing a gravity hw/pumped ch system.

If so this is on the gnd floor and will create major upheval.

so be it. I doubt its "major, running a couple of pipes to the ground floor, but whats has to be done has to be done. Better doing it properly than living with a bodge and constant maintenance.

By disaster is it a safey issue in its current config.

potentially, it depends where the vent is now. As you dont know it would be wise to be cautious.

 

[scoobydo123]

Ollie20

Unable to use the combined system as there is no safety cut out, although I believe it was an optional extra for this boiler.

Mickyg I will have another poke around to see if I can establish where the current expansion joins the system

tks