vented Hot water cylinder, CH works fine, only lukewarm DHW

[rizsher]

Have had problems with my hom central heating/DHW system since beginning of December.

The problem was traced to a leak on the flange upstream of the pump which was replaced, at which point the system seemed to have worked fine for the last 2-3 week (save a tiny weep on a joint that drips like a thimble full over a day, waiting for folk to come back in january to sort it out, thought this may be related to my current problem).

For the last 2-3 days, the DHW system barely gets luke warm; I turn on the hot water time about half an hour before the CH time to allow the hot water tank to reach temperature. Always used to get very hot water, but now its barely warm; however, if I turn on the electrical immersion heater, the water reaches temperature fine.

Are these sysmptons of an air lock, would running cold water through the hot water tap help?. Could the tiny drip be introducing air in the system?.

Is there a way to vent the hot water cylinder?. I'm almost totally ignorant of the way the UK CH/DHW system works, but can post picutres of the hot water cylinder if that can help someone guide me how to vent the air lock from it (if this is indeed possibly the problem).

Thanks for any help.
Riz

 

[kirkgas]

soundsvery much like an airlock in the hot water system, can you identify the heating coil on the cylinder? cold water from loft tank goes into the bottom of the cylinder, hot water comes out of the top so you are looking for 2 connections between these, usually in line wih each other, the top one id the flow and may have an air release on it, sometimes the same as the bleed point on the end of a radiator sometimes a flat cap the size of a 5p piece with a slot in the top (unscrew with a large screwdriver, only about a quarter turn) you will hopefully get air then water, if only water the prob could be somewhere else, a photo might help us identify what you have if this post doesnt help

 

[rizsher]

Thank you very much Kirkgas. I think your instructions are pretty clear, but, I don't want to take any chances.

Will climb into the loft again to get some pictures of the pipework and the cylinder.

If it is an airlock, does it only effect the heating side from the boiler, doesn't the electrical immersion heater get affected by the same problem?.

 

[rizsher]

OK,

Got some pictures now.

First one:



This seems to be the vent off point as it has a port with holes round the axis and a big screw on top, show in this pic:



and for completeness: The hot water outlet from the top of the cylinder:



Is this the point to bleed from?. Do I do it when the cyliner is completely cold?, i.e do I run hot water until there is no warm water coming anymore?.

Thanks again for all your help.

Riz

 

[kirkgas]

what you have is an auto air vent which is spring loaded and "should" expel the air when it builds up, sounds like yours is cream crackered, i would be very wary of trying to free it and would suggest you get 2 spanners and carefully loosen the nut where the pipe joins into the air vent, if you release it slightly you will either get air then water or just water, have the hot water on so that when you release it you can feel the hot water circulating, if you get air out give it 30mins or so and you should see an improvement in the water temp, if you dont get air out there may be another prob but give this a try first, a long term fix would prob mean a partial draain down of the system and fitting a new auto vent
re the immersor, no the prob with air in the pipe only effects the water when heated from the boiler, because the pipe has air in it water from the boiler cannot get into the tank, the immersor is directly heating the water as it is fitted inside the tank.

 

[kevindgas]

sounds more like a mid position valve problem to me or a cylinder stat set too low
check that the cylinder stat 1/3 up from bottom of cylinder (if fitted) is set to 55-60
then switch on hot water only, find the valve usually in airing cupboard beside cylinder, check that the bottom pipe and hot water out pipe get hot the C/H side should stay cool. if it doesn't then valve is goosed!
if it does then swittch on the C/H as well all 3 pipes should now be equal temperature. if C/H gets hotter than water side then again the valve is most likely faulty.

 

[rizsher]

Thanks guys.

Kevin: I've checked the thermostat, it is set at the same position its always been, 60 I think. all the pipe do get equally hot when CH and DHW are on simultaneously, its just the boiler switches off within 5 minutes or so when it is on hot water only timing.

Kirk, are you saying loosening the screw on top of the air vent will not do anything, and I need to actually loosen the whole assembly?.

Riz

 

[theheatinghelper]

hmmmmmmmmmmm i thought if u had an airlock the hotwater would run dry ??????see if you have a 3 port valve or a two port valve, when you boiler kicks in on hot water check the flow pipe coming from the 3port or 2port going into the middle of the cylinder and directly below this should be the return pipe ......after 5-10 mins ....
1) if the flow is hot and the return is cold theres a problem with the coil in the cylinder
2) if the flow pipe is cold then your 3/2 port is the problem as its not driving over for hotwater and the hot your getting through your taps is just transfer heat
3)if the flow is hot and return is warm/hot then it sounds like your cylinder stat is up the spout as its shutting the boiler off way to early.

i cant for the life of me see how a leaking flange is causing the hot water to run cold. it may cause it to run dry but not run cold ...in my eyes if there was a leak on the cylinder anywhere the boiler would keep running more often as to compensate the loss of hot water from the cylinder.

 

[kirkgas]

Thanks guys.

Kevin: I've checked the thermostat, it is set at the same position its always been, 60 I think. all the pipe do get equally hot when CH and DHW are on simultaneously, its just the boiler switches off within 5 minutes or so when it is on hot water only timing.

Kirk, are you saying loosening the screw on top of the air vent will not do anything, and I need to actually loosen the whole assembly?.

i would stay away from messing with the top part as it is meant to auto expel the air it is obviuosly jammed and will surely leak if you touch it, I would suggest you carefully loosen the coupling where the pipe goes into it as a safer bet,
PS "the heatinghelper" you are right about thinking an air lock in a heating coil will mean no water, that is what i think it is happening, it wont however stop the water flowing out of the tap as that comes from a mains fed 50-100 gallon tank above the cylinder

 

[kirkgas]

i cant for the life of me see how a leaking flange is causing the hot water to run cold. it may cause it to run dry but not run cold ...in my eyes if there was a leak on the cylinder anywhere the boiler would keep running more often as to compensate the loss of hot water from the cylinder.[/quote]

i cant see anything about a leaking flange in the original post, am i missing something?

 

[theheatinghelper]

The problem was traced to a leak on the flange upstream of the pump which was replaced, at which point the system seemed to have worked fine for the last 2-3 week (save a tiny weep on a joint that drips like a thimble full over a day, waiting for folk to come back in january to sort it out, thought this may be related to my current problem).

i read it as the flange was still leaking im sorry if i caused any confusion kirk

it just seemed like a 3 port problem to me

 

[kirkgas]

The problem was traced to a leak on the flange upstream of the pump which was replaced, at which point the system seemed to have worked fine for the last 2-3 week (save a tiny weep on a joint that drips like a thimble full over a day, waiting for folk to come back in january to sort it out, thought this may be related to my current problem).

i read it as the flange was still leaking im sorry if i caused any confusion kirk

No prob, i am easily confused at the best of time

 

[Nige F]

I thought those horrible cheapo air vents used fibre washers that expand/seal when water touches them Anyways get it changed for a proper brass bodied auto vent, as suggested Not very expensive .

 

[rizsher]

Thanks for all your help guys. I loosened the top screw a bit, got like a woosh of air for about a second and then water; that seems to have fixed the hot water. I had also raised the setting on the thermostat wrapped round the cylinder from 60 to 70, so, maybe that was what is giving me hot water. Not going to mess with it as in the next couple of weeks, I'm getting the whole damn system replaced.

What are your thoughts on Combi boilers, is there a big advantage in getting what are termed "storage combi boilers", instead of a bog-standard combi boiler?. The research I've done over the internet seems to suggest storage is obviously better, however, the location my current Worcester is installed is not deep enough to take a storage combi, would require a bit of re-modelling of the pantry where it'll get installed. So, if there is not great difference b/w storage and standard combi's, I'd prefer a standard combi, however, since this is a substantial investment, if there is substantial benefit, then I might as well get the storage.

Would appreciate your thoughts.

Thanks again.