No Hot Water after draining down system

[flutterbye]

Hi

I recently drained down my central heating system to replace a faulty radiator valve but when I filled it up I've been left with no hot water!

The hot water inlet to the cylinder is "piping hot" and the return is cold. I can't feel any movement inside those pipes by holding them and was wondering if it could be some kind of airlock inside the coil in the cylinder?

The system is gravity with pumped CH and the CH works fine. Everything was fine before I drained it down and then filled it back up again.

I'd be really grateful for any help or pointers on this!

Thanks!

 

[Softus]

Could be an air lock on the gravity side, but check first that the F&E cistern isn't dry.

If you believe that there's water in the system then turn off the CH and turn the boiler temperature up to maximum until the water flows.

If you know how to temporarily remove the boiler thermostat sensor then do that, but not if you don't know what you're doing.

 

[flutterbye]

Thanks for the reply.
F&E is at its normal level. I tried increaseing boiler temperature for 20 mins or so it just meant the entry pipe to the cylinder got even hotter. The cylinder exit is still cold.
The only other thing I can add is that the bathroom radiator was off for the last 9 months and I've put it back when draining the system but like the cylinder it stays cold. I thought it could be directly connected to the hot water but we had hot water when the radiator was out so I think a faulty radiator wouldn't be the cause of this?

 

[flutterbye]

Sorry to repeat post on this but I'm pretty desperate! If the pipe from the boiler to the cylinder is very hot but the return back to the boiler is ice cold and the cylinder isn't heating up then from what I've been told so far its an airlock in the cylinder coil?
There are no vents in the airing cupboard but I tried losening a couple of the valves to see if any air came out - only water.
I've also tried the suggestion above but my boiler will only go up to 85degrees. Could I hardwire the immerision to heat up the water to boiling or will the cylinder explode? !!

 

[kevplumb]

what boiler

 

[flutterbye]

Its a Potterton Netaheat 10-16

 

[kevplumb]

try slackening the cylinder union

 

[bab]

dont touch the immersion its not connected in any way. is the feed & vent for the heating connected to the coil inlet & outlet. Sounds as if u may need a boil at it . i guess u arent running the heating at the moment. u could rty the pump on max speed with all the rads manually switched off. depends how the pipework is on the boiler weather u have 2 returns or 1 comman.

 

[flutterbye]

There are two returns with one pump moving the rad circuit and gravity driving the heating element in the cylinder.
If there is no air on entry and exit to the cylinder coil does that mean there can't be an airlock in the cylinder?
If there is, I was just thinking of using the immersion to boil the water surrunding the coil so that the coil itself heated up to 100 and removed the airlock.

 

[bab]

2 returns 2 boiler so forget pump. airlock probably on return between coil & boiler unless some sludge has collapsed causing a blockage. what boiler & where.

 

[kevplumb]

Its a Potterton Netaheat 10-16

 

[flutterbye]

Thanks Kev!

Boiler is directly below cylinder. So are you thinking the blockage is either in the coil itself or on the return? If it was on the return wouldn't the return be warm until the point of blockage? (Its stone cold from the cylinder onwards)

 

[bab]

Sorry Kev had gone 4 a brew then. do u dare to tel him how to boil it. i dont.

 

[flutterbye]

Is there anything I can do?

 

[bab]

if u take the boiler thermostat prob out of its phile with just hot water on let the boiler run & when it starts to bubble & his turn off the thermostat to 0 and stand back to see if a load off cold water shunts down the return. its a bit alarming but will cure an air lock or even a little sludge,. u could 1st try draging a little water out of the boiler drain off while the boiler is on to see if its draining down the flow that was hot as it should drop down the return nomally.