GRAVITY FED HEATING SYSTEM - NO HOT WATER - PLS HELP! All aspects of plumbing questions and answers, help, tips and information

[Leeroy]

Hi there - hoping someone can be kind enough to help me.. I have a Gravity fed central-heating / hot water tank system powered by an old Glow Worm 52B Super boiler... for the past couple of days while the central heating is absolutely fine, it doesnt seem to be getting hot water up to the storage tak which is 2 floors up in the attic.

It's powered by a Daqfnoss controller which has 3 settings - "Heating and Water", "Water only" and "off". When it's switched to water only, for some reason it's heating up the upstairs radiators - rather than the water tank as it has done for the past 2 years.

I have had a couple of similar faults regarding lack of water in the past... however these have always been solved by going to the loft and moving pipes slightly... following a slight gushing noise, this has always solved the problem... not this time.

Any ideas on what the prob could be?? Does it sound like an air lock somewhere near the water tank?? If so, how is this solved??


Any help massively appreciated.

Lee

[Dave From Leeds]

Hi Leeroy,

You probably have an airlock in the heating coil inside your hot water cylinder. Two possible things to try.

First, find two pipes going into one side of the cylinder one directly above the other. Then slacken, but do not remove the union on the top one. This may allow the air to be pushed out by the head of water in your central heating top-up tank in the same way as bleeding a radiator. Once water starts to dribble out as well, wait until any air bubbles subside then re-tighten the connection. This may well solve your problem.

If the above doesn't work, a more complicated method would be to locate your CH top-up tank (F&E tank) This will be the smaller of two cold water tanks probably in the loft, but certainly higher than the HW cylinder. Fix one end of a hosepipe over the open end of the vent pipe that goes over the top of the tank with the other end attached to a mains water fed cold tap. Then get an assistant to slowly open the tap whilst you observe the tank from above. Air bubbles should come in through the outlet at the base of the tank. Once these stop, turn off the tap and all should be OK. Do not open the cold water tap too far or the flow of water up into the F&E tank may be too fast for it's overflow to cope.

Hope this helps.

P.S. Have the upstairs radiators heated up in the past when set to Water only in addition to the water warming up?

[Steve the gas]

Hi Lee,

Find where your motorised valve is - this is your problem I think. Either change head or complete valve, but put it on manual first to test.

Hth

[rosebery]

"Does it sound like an air lock somewhere near the water tank??"

Yes it does and if you've fixed it before by waggling pipes then that sort of confirms it. It would be as well to check that the ballvalve on the feed isn't stuck - the cylinder might be empty!

First of all I'd like to confirm that your system is a gravity system as I understand the term. Does it look like this image? Google " gasman.fsbusiness.co.uk/images/gravdhw.jpg"

If so there are two ways of dealing with an airlock in the coil. One you can do yourself annd the other needs an RGI to be safe. The one you can do yourself is to slacken off the union on the top pipe to the tank and let air out. Dave from Leeds has just described this process in his first paragraph.

The second solution involves pulling the boiler stat and boiling the air out. Do NOT try this one yourself. An RGI will know how far he can push this process without doing damage. Get the expert to do this one.

To be certain though it would really be appreciated to understand your system configuration FULLY.

I am going to be away for a job for a couple of days (from now) so may not be in a position to provide further data instantly but someone will be along who can help you further.

Cheers

[rosebery]

[quote="Steve the gas"]Hi Lee,

Find where your motorised valve is - this is your problem I think. Either change head or complete valve, but put it on manual first to test.

Hth[/quote]

@ Steve

He may not have one in a gravity HW system.

Cheers

[Leeroy]

Thanks Dave. To answer your question, no, the upstairs rad's have previously stayed off when it was set to water only, this only started happening yesterday.

Used the Emersion heater (for the first time ever) to heat the water yesterday and used all of this water for a full bath.

Had the heating on for about 3 hours last night (until about midnight) and this morning there thankfully seemed to be hot water! Can an irlock be a temporary problem? Would the pipes still need bleeding to prevent it coming back?

Steve - thanks - would the above (ie, the hotwater coming back) still be the case if the valve had gone??

Thanks

Lee

[willie gas]

hi leeroy first thing to check is, make sure there is plenty of water in header tank in loft (small tank) second i dont think you will find a motorised valve on the hot water side as u dont normanly have one on gravity hot water.

[Leeroy]

rosebery - yes, it's defo a gravity fed system like in your diagram.

The water header tank has always been full as well so no issues here.

Have come home from work, the "water only" setting has been active for 2 hours and again it seems like we're back in business with a tankful of hot water. Also pipes from and to the boiler are very hot all the way up... they weren't yesterday.

Thanks to your advice, it seems like there's an airlock in the system that comes and goes. Why would an airlock come and go like that though? If it happens again I think I'll have a go at the free DIY fix...

Thanks - all advice so far much appreciated!

[rosebery]

"Thanks to your advice, it seems like there's an airlock in the system that comes and goes. Why would an airlock come and go like that though? If it happens again I think I'll have a go at the free DIY fix..."

Air will move around the system and come to rest where it feels like it depending on where its got to and the effects of temperature cycling. I've no real explanation. Perhaps it just got bored with the view?


"Thanks - all advice so far much appreciated!"

Pleased its working now. It would be an idea to get any residual air out though.

Cheers