17 January, 2012
The Other Half was filling the sink to wash the dishes this evening when the water ran out.
I checked the loft header tank. It was empty. The main header tank on the hill was half full—about 7,000 litres of water.
I checked the flow at the stop cock where the water enters the house. It was good, so the pipe wasn’t frozen.
I methodically worked my way through all the sections of pipe leading up to the loft header tank: water was passing through both filters, water was passing through the stop cock after the filters, and water was reaching the stop cock in the loft.
However, no water was flowing from the ball cock in the header tank. I dismantled the valve. It was in good condition and no water flowed when it was removed. I re-assembled the valve.
I removed the section of pipe between the loft stop cock and the ball cock. It was clear. I turned the loft stop cock on and water flowed.
After re-attaching the pipe to the stop cock but not the ball cock, I turn the stop cock on and water flowed but only halfway up the pipe.
It appears we don’t have enough pressure to push the water through the filters and into the loft header tank. The bottom of the hill tank is about 20 metres above the top of the loft tank, which has provided sufficient head to push the water through the pipes in the past but doesn’t appear to be enough with the extra pipework.
To complicate things further, we need water to run the central heating. And the sub-zero temperatures mean our 2,000 litres of reserve rainwater is frozen solid in its tanks.
I’m now running the borehole pump continuously to see if filling the hill tank to the brim makes a difference. Fingers crossed!
Hi Stonehead.
I’d have thought your central heating system would have been a closed radiator system.
It’s an open vented central heating system with gravity fed hot water from an indirect tank. When the main water supply runs out and the hot water tank empties, the water in the exchanger boils and vents to the atmosphere. Eventually, the water in the boiler’s header tank runs out too and it boils dry. Not a good scenario.
We now have a trickle of water entering the loft tank. At the rate it’s coming in, it will take all night to fill. It looks like I’m going to have long night trying to get this sorted.
And a trickle it remains. The flow into the loft header tank is much too slow to keep up with even a single tap run slowly. If, say, the toilet is flushed, someone is showering and there’s a load of washing on, then the tank is going to empty and take hours to refill.
we have a similar set up here with headertanks in the field above the house roughly level with the house loft. We have a central heating pump attached to the main feed pipe at ground level, it is switched on by the ball valve in the loft header tank, and pumps into the loft tank. Works ok. Only problem we had was the tanks and inflow/outflow pipes froze up last year but it was in the minus 20′s. So far been ok this year
We have a double-skinned tank on the hill. The water had about 10mm of ice on the surface when the temperature dropped to the -20s, but the outlet is buried quiet deep so it didn’t freeze. The inlet doesn’t freeze as it drains backwards to about 50cm below ground when the pump stops.
A central heating pump between the inlet stop cock and the filters might be a good idea. I’ll have to check the flow rate before putting one in as the UV filter handles up to six litres per minute. I don’t want to exceed that.
Even if the water isn’t frozen the viscosity does increase at low temperatures which means that you’ll have a lower head in cold weather but I’d be surprised if that’d account for a working system failing.
If you’ve got a kitchen or outside tap connected directly to the mains is there any chance you can get a hose upto the loft tank? If that flows well then it shows that the problem is between where it comes in and the tank, if not then it’s the feed into the house – it’s possible there’s a minor blockage somewhere which is reducing the flow and hence the pressure.
There’s good pressure at the stop cock where the supply pipes comes into the house. I disconnected it and checked. It used to run directly to the loft tank and we had good flow then. The flow at the stop cock is similar to what it was then—a huge gush that cleans the floor quite nicely.
Having done some experiments, I’ve found water doesn’t reach the loft tank if we have 5,000 litres or less in the hill tank. The hill tank is about 15-20 metres higher than the loft tank so the water should flow to establish its level but it doesn’t when the filters are linked in. It comes within 10-15cm of the loft tank’s inlet and no higher.
As the hill tank fills between 5,000 and 10,000 litres, we get a steadily increasing trickle into the loft tank. Once the hill tank fills past 10,000 litres and heads towards capacity of 14,000 litres we get a decent flow into the loft tank. As this didn’t happen before we had the filters, I suspect it’s down to the way they restrict the flow.
The short to medium-term solution is to set the borehole pump up to run more frequently and keep the hill tank filled to 10,000 litres or more. Power consumption will be the same, but the pump will have to cycle on and off more frequently so it will wear faster.
Another possibility would be to put a float valve in the header tank then link it via wireless to the borehole pump, activating the pump when the level drops below 10,000 litres. I’d need a 12v set-up at the tank with a small wind turbine to charge its battery. The pump runs off the mains so that wouldn’t be a problem for powering its wireless connection. However, we’re a bit short of cash at the moment so the fancy set-up is out for now.
I’ve been looking at various ways of controlling the borehole pump to keep the header tank filled to 10,000 litres or more. The off-shelf UK systems tend to require wired controls and float valves. DIY systems can be built with wireless controls but still need float switches mounted inside the tank. And there’s the need for a 12v battery to run most of the systems.
Then I found a New Zealand company that makes exactly what’s needed: a tank monitoring unit that uses ultrasound to measure the depth of the liquid, a control unit that switches the power to the pump, and a display unit to control and monitor the parameters. Even better, all three units are connected via wireless while the tank monitor and display use AA batteries. I eventually found their UK distributor but the price is too high at the moment. It is a neat solution, though.
Back to the DIY solutions!
Your filters will reduce pressure – you should be able to find out exactly how much from the model, with a 20m head you should have about 2 bar at the loft tank which I would have expected to be more than enough for a couple of filters. (Granted I’m running these figures through my head).
One thing to check is that there’s not a pressure reducing valve in the water filters or that there’s a blockage in one of them.
Other things to think about which could help, but all are awkward.
1. Increase the diameter of the pipe up to the loft – larger diameter pipes have less resistance, but I’ll admit that this is unlikely to be valid approach
2. What sort of isolating valves do you have on the pipework to the loft? There’s a couple of different types (and their names fail me), one type interrupts the flow more than the other. Changing to the different type could help.
Fluid dynamics is a real pain.
It certainly is! Thanks for the help.
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How tall is the water tank from top to bottom? I guess 2 meters max which is 0.2 bar or 2 psi from full to empty so a pressure gauge on the filter inlet won’t be much use as a remote gauging method. Yes you have 20 meters of head but most of that is in the pipework so useless in remote gauging of the tank.
Anyway you don’t need a wireless controller as you can replace the wireless bit with a stonehead.
Fit a float switch in your storage tank at the roughly the 8000L mark. Then you need 1 small 12V solar panel, 1 small 12v battery, 1 12v bulb (rotating orange one for added comedy value). The float switch when closed will light the bulb which will be seen by the stone head who will then go and start the pump. You know how much per hour the pump kicks out so it is a simple matter to run the pump for long enough to reach 100% full.
Or you can cross my palm with pork chops and i can sell you our back-up water pump which you can use to replace the header tank in the loft
Thanks, but we’re keeping the loft header tank so we have clean drinking water during a blackout. If the electricity goes, we can just the inlet stopcock off and know we have enough drinking water for several days. We have the rainwater tanks for everything else.
Plumbers and the council officers who monitor the grant scheme all think we should go for a pumped feed from the borehole to the house with a pressure switch and no header tanks. The problem with that is there’s water supply if the electricity fails. There’s also no reserve if the borehole becomes intermittent or runs dry. I like to have backups that don’t rely on electricity. (I also have a Lister LD with a water pump, just in case. Even better, it runs very well on vegetable oil.)