Existing tank is 1200*450 which suggests probably about 150L. It's old and we have a power shower - the few times we've had people to stay we've run out of hot water.
What size would be 'normal for a 4 bed house? Are we likely to see any difference from an identical replacement cylinder? The next size up (200L 1500*450) is a lot more cash - £230 vs £160 - so we dont want to go overboard if it's not necessary
162 litres, I believe.
This doesn't make sense. Do you mean a keston system boiler, pumped for heating, gravity circulated for HW?
No. It will be identical. However, you can increase the energy storage by boosting the cylinder thermostat. This should only be done to the extent that the boiler will still heat it (i.e. still at least 10C below boiler flow temp) and that it is safe. Anything above 60C could be dodgy if there are children or other vulnerable people.
I'm worried that a 162 litre cylinder isn't enough for a couple of showers. Perhaps your system isn't reheating like it should, which is common with gravity circulation. Perhaps you should convert to a fully pumped DHW circuit with DHW priority.
Christian.
please explain run out of water was it 1) no (or little) water came out of tap 2) water came out but was cold 3) something else
It might simply be that the reheat time is too long on the old cylinder. My house has a 42x16 HW cylinder (1050x400) [1] which and the Keston reheats it in under 20 minutes.
To run out of HW several baths very quick sucession would have top be taken.
[1] This is a little narrower than the 'standard' 42x18 or 36x18 so as to fit in the rather shallow airing cupboard of my house. It has about the same capacity as a 36x18. It has a 6 turn coil. I beleive it is a nominal 30 minute heat up (from stone cold).
Is this a "combi"? If so what DHW is being instantly heated and what DHW is being fed by the cylinder? What model and size is the Keston?
About 250 litres. This can be reduced if using a large output boiler and a quick recovery coil cylinder. "Always" fit a quick recovery coil cylinder. Part L is not quick recovery, but sales counter arm wavers will tell you so.
If it has a quick recovery coil and the system is wired up to be a DHW priority system (wiring only), yes.
More info needed. What flow rate is the power shower pump?
Put on in with a quick recovery coil and you will be reheating in far less time than 20 mins.
anthony james wrote: More detail:
- it's a fully pumped system but there is a water tank in the loft which tops up the hot water cylinder.
- the pump is a Salamander 75x. Looks like it has a flow rate between
10 and 20 lgm- when the hot water runs out we get nothing from the hot tap
I suspect that part of the problem is that both the hot and cold tanks are too small, coupled with a low (london) mains pressure meaning the cold doesnt refill quickly enough.
OK, then it's time to do some measuring and arithmetic.
You need a container of known size - e.g. a large jug or a bucket and a stop watch.
Measure the rate of water use at the shower. It probably takes its cold feed as well as the hot from the roof tank so if you think the cold tank is the issue (and it sounds like it is) then the total volume is what matters, because the tank is emptying.
Then measure the flow rate into the tank in the roof. You will probably see anyway, that the tank is emptying but you will be able to work out how long it will last by subtracting input rate from output rate. The difference between the two and the volume of the tank will tell you how long - or you can simply time it.
If the filling rate really is a lot less, you can investigate why. The float valve may have crud in it or have an inappropriate restrictor or the pipework may be inadequate. You can also measure the flow rate at the kitchen cold tap to see what the mains flow rate is like. If it isn't a lot less than at the tank, then the service pipe from the street may have a partial blockage, be inadequately sized or either the stop tap in the street or the house be turned down. If there's a big difference, then the internal pipework may be inadequately sized or the float valve unsuitable. I have a low water pressure/flow problem and made some improvement by fitting two Torbeck valves to reduce the resistance at the tank. Even fitting a single Torbeck would probably help.
If there is nothing that can be done with the flow, then the only option is to increase storage. You could either fit a larger tank or a second one. If doing either, it would be a good idea to check with a structural engineer first because it should be located over a structural wall and well supported over a large area on a suitable platform. You don't want it coming through the ceiling - a lot of water and a lot of weight. There are low height "coffin" tanks on the market if that helps.
For a second tank, there is a specific way to plumb. The float valve(s) should go into one and the outlets from the other. You have a connecting pipe of 28mm size near the bottom of each. There should be an overflow from both.
Once you have resolved the cold supply, you may still have a problem of inadequate supply of hot water. There are two ways to address this. You can go for a larger cylinder and secondly a fast recovery one. This will allow for greater transfer of heat from the boiler, even while water is being used, and will effectively allow a longer run time.
.andy
To email, substitute .nospam with .gl
What is fully pumped? All the hot and cold taps are on a pump? Or is just the shower on the pump?
No hot water or no water at all?
Too small? Do you run out of hot water quickly? Do you run ot of hot and cold water, that is none out of the taps?
You could fit a larger mains pipe to the cold water storage tank. And then fit a Torbeck or Fluidmaster ballcock, whicha are available from Wickes and B&Q. These are either open fully or closed. A normal cheap brass one gradually opens. You want as much water filling the tanks as possible as soon as possible. If I understand the problem correctly of course.
Unless the original presumably 15mm feed pipe is damaged in some way, just how much difference to flow would changing this for larger make? It's a pretty major undertaking in most houses.
Given that this slowing down only effects the 'top' of the tank, I'd say you're clutching at straws.
FYI, I selected this cylinder primarily on size but made sure that the 'reheat' time was a nominal 30 minutes or less. To obtain one with a faster coil would have called for a custom order at around double the cost. It is entirely satisfctory for this house.
Technical design is not all-or-nothing or the 'without compromise' of marketing and brochure hype. In practice design criteria involve compromises and weightings.
Consider the design of a car suspension with respect to weight (lack of it),cost and functionality.
For a volume car the order is 1. Cost, 2= Weight 2= Function. For a sports car the order is 1= Weight, 1= Function 3. Cost. For a luxury car the order is 1. Function, 2. Weight, 3. Cost.
In all cases the all of the criteria are important it is their relative rankings that change.
Part L.
No one said it was.
Your compromise was based on cost and cost only. If I was installing a new expensive condensing boiler I would have gone to the extra cost of a quick recovery cylinder.
If a superior cylinder was not a special order at twice the cost (what was twice the cost?), a quick recovery cylinder was in order as they are not that much more expensive than cheapo ones. As you have a condensing boiler a quick recovery cylinder would also have been more efficient in energy terms at the return temp would have been lower for much of the run time.
It sounds as if a good high flow combi would have solved all your problems. It appears the cylinder is probably taking up valuable space.
Apologies again. I've really not made this very clear.
- Keston Condensing boiler. Sealed system. Indirect coil on a 160L hot water tank that refills from a cold tank in the loft.
- Salamander pump on the shower only.
- when the hot water runs out nothing comes out of the shower or the unpumped taps.
Without needing to do any calculations it's pretty obvious to me that the shower pump will easily draw off more water than will come in off the mains and it's pulling off both the hot tank and cold tank (whick is simultaneously trying to refill the hot).
There's no practical/affordable way to improve the supply to the house
- the 15mm pipe would not be easy to replace. we're installing a better stopcock which might improve things.
Making both tanks larger would seem to be the solution. Hot is easy, cold might need a bit of thought as it's location is not ideal and our joists are a bit on the weedy side.
Ok. We still need a bigger tank because however quick the recovery it's not going to help if we're taking water out much faster than it's going in.
Can you point us in the right direction - looking at discountedheating.co.uk i dont see anything clearly labelled "quick recovery". The pressurised tanks mention it but they are many hundreds of pounds more expensive and would likely need significant replumbing.
Fit a full bore valve.
Terminonlogy:
- Cold water storage tank
- Hot water storage cylinder.
Making both larger would not necessarily be the easiest way. It appears only the cold water storage tank needs to be larger, if you cannot re-fill it fast enough by doing:
a) Fitting a full bore stop c*ck on the mains and on the pipe feed the cold tank. b) Fitting a Torbeck valve on the cold tank.
Do the above first and see how it goes.
Do the above first, as I have suggested. If still problems then replace the cold water storage tank, or add another. If still problems, this should be hot water running out (turning cold), not water running out, then fit a blending valve to the cylinder draw-off and set it to 50-55C and turn the cylinder thermostat to 70-75C.
See my other post on this.
Travis Perkins do a good deal on the Telford Typhoon quick recovery at aprox
160 litres. This will do you when fitted with a blending valve on the draw-off. Blending valves are to become mandatory next year, so you can jump the gun.
Somehow I doubt that even if you knew all the cicumstances surrounding the choices made for this heating system you would revise your "high-flow-combi fits all" stance.
A poor water main using iron pipes running for some length in someone else's home, was one of the factors. Another was the difficulty of flueing. Another was 'her' wishes.
I expect you will have some scathing words of reply.
"high-flow-combi
No. Just that her wishes should be taken into account.
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