Head of water in vented system

Bungalow built in the 70s with a vented system. Impossible to raise the storage tank level which is already in the roof space. Everything has worked fine for over 20 years since we moved in , with gravity fed hot water taps through the property and power showers. Recently, and this has been examined by a number of plumbers without success, air has been getting into the gravity hot water flow and causing serious water flow failures. The height difference between the header and the hot tank is minimal. If I fit a pump, will that simply draw more air - presumably from the vent pipe (nowhere else for it to come from) ?? We are struggling here. Oh - and mains water pressure is excellent. So no problem whatsoever with storage tank capacity.

 

Nothing has been changed in the past several years. There has always been a power shower, which has been replaced with a new one a few years ago. Unbelievably, our problems started after the fitting of a new ball valve to the cold storage tank which was not sealing properly and the overflow was dripping rapidly. After that we had incredibly noisy pipes. We use a "plumbing insurance" cover and they have visited many times recently, first to fit the new ball valve, then to sort out the noises, now several times to get us hot water back into the taps. They suck out the air, and it lasts, at best, for a few days, but is getting worse. Initially it was a failure in one hand basin, then another, and finally, this week, every hot tap in the house. The plumber came again yesterday - with his vacuum pump and got it flowing again. It really is unbelievable. The plumbers are confused - to say the least. One suggested fitting a pump - but my concern is that the pump would simply draw more air. Oh, the power showers are both dual feed. I don't know about "flanges" I am not a plumber!

 

No problem with the inflow to the cold tank. Every plumber who has been to look assures me that the inflow is far greater than any potential outflow with taps or showers. We really do have very good pressure on the rising main. Both showers have their own inbuilt pump to provide shower pressure, both are dual feed. The thought that there could be an emptying of the cold tank was one of the first things on my mind - but I am assured that it cannot be the case. I am also assured that the only possible air intake is through the vent. I am considering possibly moving the entire hot-water cylinder to a lower point in the house. It is currently also in the roof space, and as I indicated in my first comment, the "head" is pretty much at a minimum. I don't want to go to a massive expense - if it can be avoided. The nearest possible place for the hot cylinder is probably some way from its present location - if we could squeeze it in there, above the oil fired boiler.

 

Accepted. It does seem coincidental. The ball valve was replaced 15 months ago. It is now a long on-going saga. I have lost count of the number of visits made by qualified plumbers employed by the insurance company. I need closure. Already, after yesterday's visit, the water in one hot tap is reduced to a trickle. This cannot continue indefinitely - hence my appeal to this forum for possible ideas. I am very grateful for your responses. I do need answers.

 

No. It is always above the water level

 

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No - there is good clearance there. We have been scratching our heads trying to think of somewhere else that we could locate the cylinder - and re-plumb the whole thing to give it a greater head, but that would be difficult. Other ideas are to scrap the cylinder system and fit an electric combi (there is no gas in this area) - or even fit a domestic hot water heater (without touching the central heating - which seems to be fine) or if possible, fit a combi electric, but only utilise the domestic hot water part of that - with the potential to connect in the central heating should our oil boiler die in the future. or when the oil in our 3000 litre storage tank runs out! Oil fired combi boilers seem to be more expensive than the others. Nothing is going to be cheap so far as I can see. I just wish I knew exactly what the insurance plumbers have actually done - because they do seem to have generated this situation in some way. I would normally have watched everything - but with lock down and distancing it has not been possible.

 

Hi, thanks again. I have made that clear to them each time they come. Their suggestion of fitting a pump on the hot outlet to improve flow did not solve the problem of air ingress - and I would presume it would only increase it. The oil boiler heats both water and central heating. There is also an immersion heater in the cylinder - but that is only used when we need more showers - such as when guests are staying. (Not happening in lockdown). The insurance company are sending out a plumber tomorrow - who will be on video call to his manager to discuss next steps. (The manager was going to come as well - but has cried off) I have made it clear that I want this saga to end. I wanted to get as much info as possible before they come, so have been trying to research all the alternatives which might apply. Asking you guys is a part of that. Our oil boiler is around 18-19 years old. It is serviced annually and that was only about a couple of months ago, but we do need to consider its possible demise. Going for a new oil system , given the present national incentive to move away from fossil fuels would seem foolish, hence looking at electric alternatives in the long term. The hot water flow normally has always been adequate, but not strong. Bath filling would take a little longer than it should, but was passable. That is no longer the case. It would almost be quicker to boil the kettle - then add cold! Thankfully we don't use it - but some guests do. We are in Worcestershire, about 10 miles west of Worcester city. In the middle of nowhere!

 

I have to admit that I am impressed by your willingness to help like this. Thank you. The hot water in the taps, since the insurance plumber tried to fix noisy pipework, following the replacement of a ball valve in the cold tank, gradually fails, over several days, before petering out altogether. It is not something which is immediately apparent when the shower is used. All they have really done since then, is repeatedly to suck out air from the system, which returns water temporarily to the taps - for a few days. There is air ingress. I have my own suspicions that this is caused by the power-shower pump drawing a little air with each shower. Maybe changing the angle of the tee off to hot water system from 90 deg to 45 deg - pointing downwards, would prevent any collection of air? In other words any air drawn in, would naturally vent itself back into the vent pipe?. The only place that air can come from is the vent pipe and it seems must be caused by the difference in levels between the cold storage level and the top of the cylinder. Why this problem has started to happen after sorting out noisy pipes - is a mystery. I am really beginning to think that the only answer is to seriously change the plumbing layout. I will be having a serious talk with the plumber this afternoon when they come for the "nth" time.

 

Sure, Thanks for that. It has been considered and may well have to happen in the future. Unvented systems are the modern way to go. That would probably be done when and if the oil boiler has to go. In the interim, there are two plumbers in the loft right now (the manager did arrive a few minutes ago) I will see what they manage to achieve. They are as frustrated by this as we are. So maybe desperation will get them to find a solution without me forking out several £K just now. I mentioned the angle of the hot water connection from the vent pipe - and suggested they just check for any potential pockets below that. We will know more after today! (Hopefully!)