Help please

[plumb-tech]

Hi all, got a little problem with a job im on.
drained down central heating to replace 4 rad valves (combi boiler). filled system back up but no heating comes to the rads downstairs, upstairs is fine, ive tryied everything i.e shutting all rads but 1 to try remove air, when i do this the rad does get hot but takes ages, if i do the same upstairs rad gets hot instantly. so i think it could be full of sludge downstairs from when i draind down.
any help appreciated.
Also if im to clean out sludge do you think its fair i tell customer its gonna cost more as i quoted her a set price.
thanks

 

[Johnno]

I have had this problem every time I have drained down for one reason or another. For me, it appears it is a water lock, where the hot water from the upstairs tries to push the cold water down stairs back to the boiler. Try getting upstairs rads hot then shutting both their valves but leave the boiler firing. Drain out of the lowest drain cock on the system until hot water comes out. You may need to do this a couple of times, during which you may find hot, then cold then hot water comming out. It has allways worked for me.

 

[plumb-tech]

Hi cheers for the reply, do you not think it may be sludge, also the boiler is upstairs, the flow pipe coming down in the kitchen gets hot but the return doesnt.

 

[wnjswozo]

It wont be sludge on a ,combi system needs balancing

 

[dontknowitall]

This is also symptomatic of a pump failure. I'm eager for responses too as I repaired a leak last week and the same thing happened to me although some heat is in the downstairs radiators. I'll be returning next week to see if it is the pump or something else.

Thanks for that tip Johnno - worth trying as if it's not the pump (and it's definitely not sludge in my case) perhaps it is a water/air lock.

 

[wnjswozo]

could be pump,some combi pumps are modulating ,so you may need mfi to test

 

[Bernie2]

If its a combi sealed system, they are usually slow to corrode, unless of course you have a lot of air entrainment. Its why they use barrier pipe if its plastic, ordinary plastic sucks in air through the walls. The gravity open vent systems can suck air down the vent or like sealed systems through worn valve glands.

The next thing to wonder about is air locks.

Just bleed system until water running clear, topping up the boiler as you go, or over pressure it and then let it come back to normal as you bleed.
Go to the furthest away rad to bleed if you have already part bled the system, or start at nearest to boiler then work away bleeding them as you go. Another sealed system trick is leave it connected to the main and open the drain offs right up letting the water flow through the system, like the car mechanics do when they renew the brake fluid.
Shut drain offs then drop pressure through prv.

It might be the pump?

Hot water will rise by itself, so the upstairs may get hot and the down stairs stay cold if the pump goes. Check pump is working.

The system may need balancing.

It could be so many things its a bit hard to give a clear answer. but basically all you are doing is pushing water around in a circle, just think of what could stop it going around and have a look there.

 

[plumb-tech]

Hi cheers for the replys. I already checked the pump its fine and i already done the thing with the drain cock, i went back today and put cleaner in and it works gonna go back tomorrow to drain and re fill with clean water.

 

[stevetheplumber]

Hi cheers for the replys. I already checked the pump its fine and i already done the thing with the drain cock, i went back today and put cleaner in and it works gonna go back tomorrow to drain and re fill with clean water.

as boiler is upstairs this isnt a pump problem have you tried shutting all the upstairs rads and all but one or two downstairs ?

 

[RoryD]

Actually you can get sludge in a combi system as it may have been installed onto a "dirty" system. I'd go with the pump idea and maybe a shot of Fernox F1

 

[david williams]

combi /system /vented / if not flushed after instalation and inhibiter put in .system can produce enougth muck in first 6 hours of running to seize pump.