This has been driving me mad. We have an open vented system, with both header tank and cylinder in the loft. The problem we have is that somehow air keeps getting stuck in the hot water pipes feeding the taps e.t.c. throughout the house. This has been happening for a number of years however I want to finally fix it. The air is most noticeable when in the shower (mixer style with cold feed from the header tank and hot from 15mm pipe connection under the bath) because while having a shower water pressure will be low and the shower will gradually get colder as the hot pressure seems to drop, forcing you to have to keep turning the mixer to a slightly hotter setting in order to maintain the same temperature. The taps only splutter air if you 'dislodge' the air in the pipes by turning a hot tap on and then off quickly again, then on, and off, each time the tap is turned back on it coughs and splutters and with any luck will eventually run at full flow. I have checked common issues such as ball float in the header tank, turning the bath tap on and making sure the header tank does not drain quicker than it fills e.t.c. all are fine. I have tried draining the header tank down and filling the system backwards by connecting the mains cold feed in the kitchen to a hot tap. The system works perfectly for about 3 days with no air or pressure dropping, but after about 4 days the air comes back. Could the vent pipe not be wide enough or long enough? Any help appreciated, this is really annoying.
I think a bigger cold tank is needed, because you say the cylinder and cold tank is in the loft I get a mental picture of the cold tank being on a stand, as a standard cylinder is 3 feet high plus a stillage is needed, that does leave much room in a standard attic for anything bigger that a 25 gallon tank, so i would suggest reinforcing the stand and get a coffin tank with a 50 gallon capacity, sorry about the imperial measures, I'm English,
The cold tank is mounted directly above the cylinder on a wooden stand supported by the brick wall below the cylinder and the eaves, not much we can do in terms of height as you say as the top of the tank isn't too far away from the eaves above.
hi the air may be draw in the system via the vent pipe. if the cold water into the tank keeps up with the flow out, the vent pipe may be the problem. it is possible to re-pipe the vent to overcome this regards peter
Try to post a photo Of the cylinder, tank and surrounding pipes - espec the vent one. (I suspect it might be as Kiaora says; the vent comes off the top of the hot cylinder - where the hot water is also drawn off. A downstairs tap will cause a lot of draw from there, and if the cylinder isn't being refilled fast enough to cope, 'suction' could empty the vent pipe and draw in air. If so, how would you re-route the vent pipe to prevent this?) Just re-read Jonatahn's first post - he says it happens most when using the shower which only has a 15mm hot supply pipe. Weird - that would struggle to empty the vent pipe and draw in air, wouldn't it? Unless - it's the normal taps - bath, etc - which actually draws in a bubble of air, but the symptoms only appear when using the 'slower' shower? Ach - it's a mystery...
Good thinking, i'll upload a pic soon once I have taken one. From memory the pipe comes out of the top of the cylinder, bends downwards almost towards the floor of the loft, and then runs on a slight slope downwards towards the bathroom wall, along with the central heating piping e.t.c. The vent comes off the the sloped section, close to the tank and loops up and into the cold water tank. In terms of Air / pressure issues: (See Diagram) The shower does not seem to cough or splutter, unless forced to. The hot taps in the bathroom are the ceramic valve style? Correct me if I am wrong, basically the type without rubber washers. If the sink tap is turned on and off quickly many times it begins to cough and splutter for ages, pulling all of the air out of the system. It is harder to make this happen with the bath tap. Volume of water maybe? It's even harder to make the taps downstairs splutter because they are the rubber washer style so require more than 1/4 turn to open and close fully, like the ceramic ones upstairs. If the taps in the bathroom are just turned on individually, without being turned on and off, they will not splutter. If the sink tap is open to full flow, and then the bath tap is turned on slowly, to full flow, the pressure in the sink tap will drop, and eventually it will cough and splutter until the bath tap is turned off. However, the header tank is still filling as quickly as it is emptying!! See attached diagram. The connections for the shower cubicle & ground floor are all made under the bath, stepping down in size after the bath tap connection to 15mm piping.
Hmm, strange. The one pipe you haven't mentioned is the cold supply from the tank to the bottom of the hot cylinder - that would need to be an equally easy path so's to keep the cylinder fully supplied. If that vent pipe were transparent, you'd probably see the water level inside bobbing around as taps are turned on and off. It could be that when a tap is opened quickly that the sudden draw will for a brief moment empty that vent pipe before the cylinder gets a chance to start supplying full flow as it should. You then have a bubble of air sitting around one of these pipes and it might not cause any issues until a certain tap(s) is opened a certain amount! Hey - I'm searching for ideas, here... Bottom line - it seems pretty clear that air is getting drawn into your pipes, and really there's only one place that can happen! (Unless the cold tank is allowed to empty - which it isn't...) I'd have a looksee at the pipe from the cold tank to the bottom of the hot cylinder. Does it have a gate valve on it? Is it fully open? Are you sure...?
Gets some pics uploaded but my money will be on the vent pipe being badly laid out,but I'm not going to argue with DA because he can make me look very stupid at a click of a few buttons.
The gate valve has been opened / closed recently and seems to work well, stops flow completely and does not drip. The only thing I could think of is back in around 2005 the black insulation bag on top of the cold water tank fell into the tank and stopped flow completely because it covered the cold feed to the cylinder as it wasn't supported well. When this happened some fiberglass did fall into the cold feed pipe to the tank. We removed the immersion heater from the cylinder at the time, however couldn't see any in the tank. Surely this could not still be stuck in the gate valve to this day? Also the gate valve has been operated a dozen times since then. The pressure & flow seems to be high if the system is backwards filled via the cold feed in the kitchen, however air seems to return after about 4 days, causing the pressures to drop and the taps spluttering if turned off and on quickly.
A few small points, but will your system empty twice as fast as it fills up. The hot water vent usually comes off the top of the cylinder. Your hot water will get colder as the cylinder fills up. (Ask my daughter !!). We have a similar system and every now and then we get a go slow. I just blow back mains water pressure up the hot tap (mixer) in the kitchen. Good Luck.
Jonathan, systematic approach/ process of elimination... There is air in your hot system? Yep? Yep. 'Cos the flow slows down and it goes 'cough splutter'. How does it get there? Surely only two realistic possibilities... One is that the cold supply tank is drained empty when you run a hot tap so's water gets drawn in to the supply pipe to the hot cylinder - ie: because the cold tank doesn't fill fast enough to cope. But this doesn't happen here. The other possibility is that air gets drawn in the vent pipe when a hot tap is turned on, probably suddenly and full-on. This happens because the cold supply to the hot cylinder is somehow not up to coping with this sudden demand. Why? I dunno. Possibly because of poor pipe routing. Or because the gate valve isn't fully opening for some reason. Or because of insulation caught in the gate valve or pipe ... I know it's a hassle as you'd have to fully drain the hot cylinder so's you can remove and check the gate valve, but it does beg checking, doesn't it? If it's clear, then you might get a cure by raising the cold supply tank higher if you can. That's a guess. A Mickey-Mouse solution would be to fit a gate valve in the hot water take-off from the hot cylinder (AFTER the vent tees off!) and to tweak it down a little, not enough to be really noticeable at the hot tap, but enough so's the cold supply feed from the cold tank always copes with hot water draw-off.
A blockage like fibreglass/cylinder foam floating around inside the cylinder would mimic an air lock. Around 12 years ago I had a spate of circular black plastic disc that would break away from the cylinder and float around inside giving exactly the same symptom. Tappy,
Thanks for all of the advice! It's looking more likely to be the insulation than physical piping issues. I convinced myself fiberglass wouldn't have stayed around for that long though! Best methods for draining the cylinder to remove the gate valve as there is no stopcock / drain towards the bottom of the tank? The cold feed literally enters the gate valve, leaves the gate and then is connected directly to the cylinder via an elbow piece with no drain valve.
Remove immersion heater and drain via a hose syphon? But you'd still need to run off a few inches of water from the top... I dunno...
turn off cold water, drain the cold water tank by opening all the hot water taps, when the taps stop running undo the top cylinder union, a little water will come out have a towel ready, then shove a lenght of plastic 15mm to the bottom of the cylinder, this will ensure the syphon empties the whole cylinder, attach a hose to the speedfit pipe, no need for any fitting a garden hose will push on and seal, take tuther end of hose to a drain anywhere below the bottom of the cylinder and suck, you only need one big suck to get the water above the cylinder top once you've got it that far put the hose down, you might think its not worked, but wait, its coming, don't keep sucking or you'll get a mouthfull of brown sludge,
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