Please help, big problems!!

[lyndz81]

All of a sudden I have no hot water! there is cold water coming out of the hot taps but no hot. The cylinder is cold as are all the pipes surrounding it. The radiators were working fine. I have a back boiler with an open vented system with an indirect self filling and priming cylinder. I have been told there might be air in the system. Today we have drained the entire system by tying the ballcock up in the tank to stop it re-filling and opening the drain valve at the lowest point, when it was emptied i let it fill back up and bled the raditors starting with the downstairs ones, now i have no hot water and the radiators are cold, the feed pipes to the radiators are warm. do the radiators now need balancing, and how can i solve my original problem of no hot water!
any help would be greatly appreciated.
Lyndsey

 

[ollski]

does that mean you have a primatic cyliner with only one tank in the loft?

 

[lyndz81]

i have a primatic cylinder, but i checked yesterday and have no tanks in the loft

 

[chrishutt]

Today we have drained the entire system

Why?

If the problem is an air lock, you want to vent air, not drain water. I have heard that it's important to let a primatic (self feed) system fill very slowly. I don't know why, but it might have some bearing on your problem.

I assume you have gravity circulation between boiler and cylinder. So if these pipes are air locked, you need to look for any possible high points where air could be vented. As for the CH side, you have a pump which can be used to help clear air locks, for example by turning up the speed switch.

 

[ollski]

i have a primatic cylinder, but i checked yesterday and have no tanks in the loft

Well on top of the cylinder or somewhere there will be a storage tank. You need to fill these cylinders slowly otherwise you will blow out the air lock, then you will need to bleed the system from any bleed points.

 

[Slugbabydotcom]

Losing the airlock in a primatic cylinder will usually result in dirty brown water coming out of the taps. It wont stop the cylinder from heating up.

What can stop a cylinder heating up is an airlock in the gravity circulation pipes >> this is highly unlikely seeing as they worked for so long till now although I have heard of one instance. Look on the flow pipe to the cylinder for an air vent ... again unlikely but they are sometimes there.In the instance I heard of; the airlock was cleared by loosening the nut next to the cylinder on the flow pipe, carefully breaking the joint and making it again quickly when the air was out [ A scary task ].
Please remember I cant see your system from here and it is amazing what you can find on some installations.

More likely is a blockage on the gravity circ. pipes probably near your boiler and probably caused by sludge. Draining from the boiler could be helpful in clearing it. Some back boilers have an injector tee which is a likely place for the blockage
Try turning your boiler stat up to max before you go ripping the system apart it may just blast the blockage out

When you drained the system last time you introduced a new airlock to the heating side of the system. Closing all the radiators bar one and going round ensuring that there is one rad open all the time should clear it.

 

[ollski]

yes sorry I don't mean blow it out, if you fill too fast the air lock will be too big and will prevent your flow and return from circulating like you have already, the top pipe will be red hot and the bottom pipe stone cold.

 

[chrishutt]

if you fill too fast

What is "too fast"? With float valve filling as normal? What is correct speed?

 

[Agile]

This is amazing, yet another person who thinks they have air in the system and starts by draining it all off!

Many DIYers seem to do that! If there is air in the system you need to keep the water in and get the air out! Draining is filling the whole system with air!

Tony

 

[Slugbabydotcom]

yes sorry I don't mean blow it out, if you fill too fast the air lock will be too big and will prevent your flow and return from circulating like you have already, the top pipe will be red hot and the bottom pipe stone cold.

Sorry to be the one to pull you on this oilski but that to me sounds like a load of bolllox. The airlock inside a primatic is the design size and thats it .... any excess air is vented off hence the term single feed and vent.
Thanks for being wrong about it though because it just made me think a bit harder and I realised that if the internal vent was blocked then the situation of too much air causing the problem you describe could occur

 

[ollski]

Okay I'll do some homework on the technical aspects...all I can tell you is that the original fault would have been fixed by draining and refilling the cylinder slowly.