Quizzes & Puzzles3 mins ago
Very little hot water at a time
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I have a Potterton Profile 60e boiler, which is about 13 years old. Had it serviced today by N Power, no problems. I asked the engineer why, when I run bath water, I only get about 2 inches of hot waterbefore it goes cold. If I sit and wait about 4 mins, I get another 2 inches of hot water and so it goes on. He looked at the cylinder in the airing cupboard and said it was not a conventional water heater, it was a "thermal store",. He said these are fitted in a lot of new houses, but usually with a combi boiler, not a normal boiler as I have . He suggested I should ask the manufacturer what temperature the thermostat on the cylinder should be set at. I have it at 65 degrees at the moment. The only name on the cylinder is Heatlag Green, but cannot find them on any website. Dont know if this is the company name or just name of cylinder. I have my control on the boiler set at 5 which he said was about right. Does anyone think I should try turning up the thermostat to 75 degrees? He said I should check first but I cannot find anyone to check with. Help!
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A thermal store is a lagged tank through which your hot water pipes run. These pipes come directly from the cold water mains supply. As the cold water passes through the thermal store, heat passes from the water in the store (cooling it) to the cold water (heating it) from where it passes into your bath. If the water only heats for 2 minutes before running cold, one of 2 things is wrong:
1) the thermal store is simply not big enough - these things are large - mine is a massive 200 litres, but it also feeds the CH system. If the store isn't big enough, there is isn't enough hot water stored in the tank to give a decent bath before the temperature of the whole thing falls to an unacceptably low level (to get a decent bath). Reheating the thermal store occurs via the boiler but takes time. I think this is less likely/
2) there is no aggitation of the water in the thermal store. What one typically needs with a thermal store is some pump to churn the water around inside the tank. What happens is that the hot water in the immediate vicinity of the cold water pipes give up their heat (and that give you that first 2 minutes of hot water) but the lack of movement of water in the store means that although there is plenty of hot stored water, it is nowhere near the area where the heat transfer is occurring. Result - cool water emerging from the hot tap until 'natural conduction' shifts the thermal store water around - and you get another 2 minutes of hot water.
1) the thermal store is simply not big enough - these things are large - mine is a massive 200 litres, but it also feeds the CH system. If the store isn't big enough, there is isn't enough hot water stored in the tank to give a decent bath before the temperature of the whole thing falls to an unacceptably low level (to get a decent bath). Reheating the thermal store occurs via the boiler but takes time. I think this is less likely/
2) there is no aggitation of the water in the thermal store. What one typically needs with a thermal store is some pump to churn the water around inside the tank. What happens is that the hot water in the immediate vicinity of the cold water pipes give up their heat (and that give you that first 2 minutes of hot water) but the lack of movement of water in the store means that although there is plenty of hot stored water, it is nowhere near the area where the heat transfer is occurring. Result - cool water emerging from the hot tap until 'natural conduction' shifts the thermal store water around - and you get another 2 minutes of hot water.
Part 2
I think it is the latter - not the former.
A couple of questions:
1) Has it always been like it?
2) Does the boiler come on within, say, 20 seconds of you starting to draw that first 2 minutes of hot water off?
If the answers are 'no' and 'no' then there is something wrong with the aggitation system that I describe.
The trouble with faultfinding these things is that plumbers aren't very familiar with them and every system is different in design - though the concepts are as I describe. You really need a decent heating engineer - not a common-or-garden plumber. Some systems have a separate aggitation pump (to the main pump that shifts hot water through the boiler).
I believe the above is the long term solution to your problem, however the answers to your specific questions are as follows:
You can try turning the tank thermostat up to 75 - it will do no harm. You will have to run the boiler on max setting to do this (because you need about a 10 degree temperature differential between the tank and the boiler cut-off). Monitor it and see how much water you get before it loses temperature. My guess is that you will get hotter water from the tap, but the time before it cools off will be unchanged.
Lastly I do hope my technical explanations are OK for you. Happy to answer further questions.
I think it is the latter - not the former.
A couple of questions:
1) Has it always been like it?
2) Does the boiler come on within, say, 20 seconds of you starting to draw that first 2 minutes of hot water off?
If the answers are 'no' and 'no' then there is something wrong with the aggitation system that I describe.
The trouble with faultfinding these things is that plumbers aren't very familiar with them and every system is different in design - though the concepts are as I describe. You really need a decent heating engineer - not a common-or-garden plumber. Some systems have a separate aggitation pump (to the main pump that shifts hot water through the boiler).
I believe the above is the long term solution to your problem, however the answers to your specific questions are as follows:
You can try turning the tank thermostat up to 75 - it will do no harm. You will have to run the boiler on max setting to do this (because you need about a 10 degree temperature differential between the tank and the boiler cut-off). Monitor it and see how much water you get before it loses temperature. My guess is that you will get hotter water from the tap, but the time before it cools off will be unchanged.
Lastly I do hope my technical explanations are OK for you. Happy to answer further questions.
What a star you are builders mate. Yes, I understand what you are saying as the guy from N power did explain the very basics. I will have to get back to you on whether the boiler comes on within 20 seconds, but yes, it has always been like it, ever since we moved in 5 years ago and it has driven me potty. Successive plumbers/central heating guys have all sort of scratched their heads and looked bemused. I don't know how many litres in the tank, all I can say is that it is a great big thing about 4ft tall with what appears to be a small tank on top about 18 inches tall. I will get back to you on the 20 seconds bit when there are 2 of us in the house to find out, so I can run the tap, while my significant other stands by the boiler. If push comes to shove, we will have to get an expert in as I have no idea if there is a pump inside the tank. Obviously, there is one to pump the water round for the central heating. Will try turning it up, but I think you are going to be right, and I am going to be disappointed. Will be in touch again soon, but meanwhile, many many thanks.
Obviously I can't fault-find at a distance. I don't know what a Heatlag Green is but will try and research during the day and see what turns up. Nor do I know what the small tank on the top is. How does your CH work - off this thermal store as well?
Armed with my above explanation, I hope you can see how this kind of defect can arise. But last night I had another thought to mention (but which won't please you). If you live in a hard water area, most thermal store systems recommend/insist that you also have a water softener installed at the cold water inlet. This is because, as the cold water passes through the thermal store and 'heat-exchanges' energy with the existing hot water in that thermal store, the conditions are right for the formation of scale on the inside of the cold water pipes that run through the heat exchanger (its the same principal as the scale that forms on the kettle element but in reverse - the 'hot' is on the outside - the 'cold' is inside - but as the cold gets warmer it gives up some of its limescale. The only place it can go is onto the inside of pipe the warming water is running through).
A thick layer of scale, unfortunately, is notoriously bad at conducting heat - so the heat transfer process is slowed up.
The same is true of an immersion heater installed in a hard water area - but these can be extracted out of the side of the tank - the heat exchanger in a thermal store unit cannot (normally).
Please don't take my '20 seconds' comment as kosher. All I mean is that, in a very short time - seconds not minutes, the thermal store should be detecting that it's temperature is falling fast - and forcing the boiler to start to regenerate the heat in the store.
Armed with my above explanation, I hope you can see how this kind of defect can arise. But last night I had another thought to mention (but which won't please you). If you live in a hard water area, most thermal store systems recommend/insist that you also have a water softener installed at the cold water inlet. This is because, as the cold water passes through the thermal store and 'heat-exchanges' energy with the existing hot water in that thermal store, the conditions are right for the formation of scale on the inside of the cold water pipes that run through the heat exchanger (its the same principal as the scale that forms on the kettle element but in reverse - the 'hot' is on the outside - the 'cold' is inside - but as the cold gets warmer it gives up some of its limescale. The only place it can go is onto the inside of pipe the warming water is running through).
A thick layer of scale, unfortunately, is notoriously bad at conducting heat - so the heat transfer process is slowed up.
The same is true of an immersion heater installed in a hard water area - but these can be extracted out of the side of the tank - the heat exchanger in a thermal store unit cannot (normally).
Please don't take my '20 seconds' comment as kosher. All I mean is that, in a very short time - seconds not minutes, the thermal store should be detecting that it's temperature is falling fast - and forcing the boiler to start to regenerate the heat in the store.
Many thanks again builders mate. I turned on the hot tap on the bath while himself stood next to the boiler downstairs. We let the tap run for about 5 minutes and the boiler had not fired up. Yes, we are in a hard water area so more doom and gloom. I really appreciate all your advice and efforts on my behalf. At least now when I phone someone to sort it out, I will be able to explain it much better than I could before. Regards, foxyferret
OK then. One last post to try and explain a bit further how these systems work, then I'm afraid you will have to try and find someone locally to diagnose specifically what is causing yours to malfunction.
You remember I referred earlier of the need for some pump to 'aggitate' the water in the thermal store around, so that the store's hot water is constantly kept in contact with those heat exchanger pipes when the DHW is running and being heated up as it flows through the pipes on the 'other side' of the heat exchanger? This pump is either a separate pump that only does aggitation (it will be mounted on the side of the store) or it also doubles as the main pump that pumps water past the boiler, where it gets reheated and flows back into the store. The very fact that this main pump is running and moving water in/out of the store 'stirs' the rest of that stored water up - creating the necessary aggitating effect.
Yours is definitely not doing this, and that is why it takes such a long time to reheat the DHW because it relies on slow natural convection of the stored water (hotter water gradually rises to the top, cooler falls).
You remember I referred earlier of the need for some pump to 'aggitate' the water in the thermal store around, so that the store's hot water is constantly kept in contact with those heat exchanger pipes when the DHW is running and being heated up as it flows through the pipes on the 'other side' of the heat exchanger? This pump is either a separate pump that only does aggitation (it will be mounted on the side of the store) or it also doubles as the main pump that pumps water past the boiler, where it gets reheated and flows back into the store. The very fact that this main pump is running and moving water in/out of the store 'stirs' the rest of that stored water up - creating the necessary aggitating effect.
Yours is definitely not doing this, and that is why it takes such a long time to reheat the DHW because it relies on slow natural convection of the stored water (hotter water gradually rises to the top, cooler falls).
There is one more thing you can try to get a longer shower.
Just before you go to the bathroom, go into the store cupboard and turn the thermostat up by say 5 degrees. This should force the main pump (and boiler) into action - in an effort to bring the whole store temperature up. Whilst you are having your shower, the swirling action should then be constantly mixing hotter water around the store heat exchanger, enabling that longer shower / bath run.
If that works, at least you have a solution of sorts to the problem. Of course, you can turn the thermostat down again after the shower.
The way some systems work is using a water flow sensor in the DHW pipe. Immediately anyone runs DHW, this sensor forces the aggitating pump into action. Either you don't have this sensor (a design fault) or you have it but it isn't working.
If you try my idea but still don't get any improvement in the time before the initial hot water runs out, I fear those crucial heat exchanger pipes may be partially furred up.
Good luck. BM
Just before you go to the bathroom, go into the store cupboard and turn the thermostat up by say 5 degrees. This should force the main pump (and boiler) into action - in an effort to bring the whole store temperature up. Whilst you are having your shower, the swirling action should then be constantly mixing hotter water around the store heat exchanger, enabling that longer shower / bath run.
If that works, at least you have a solution of sorts to the problem. Of course, you can turn the thermostat down again after the shower.
The way some systems work is using a water flow sensor in the DHW pipe. Immediately anyone runs DHW, this sensor forces the aggitating pump into action. Either you don't have this sensor (a design fault) or you have it but it isn't working.
If you try my idea but still don't get any improvement in the time before the initial hot water runs out, I fear those crucial heat exchanger pipes may be partially furred up.
Good luck. BM
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