Improving pressure in direct heating installation

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Ricardo Da Silva

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My flat suffers from poor mains pressure and we have a direct heat setup with combi boiler.
The boiler is rated up to 3Bar, so I was thinking of installing a cold water tank to feed a twin pump supply cold and into the boiler for hot (both 15mm).
My questions are
Is this a feasible setup
Can I use a single 28mm feed from the tank to a double 15mm manifold into the pump or should I install two 22mm/15mm feed pipes from the tank instead.
Thank you in advance for any help you can offer.
 
Thank you. Could you elaborate on why it would not work please.
If the tank is located in the loft and if a use a 3 Bar-per-side pump. My reasoning is that the pump should kick in when the cold is turned on giving me 3 bar directly. Same for the hot except it will pass through the boiler first which is rated up to 3 Bar
 
If my post you will note "so I was thinking of installing a cold water tank to feed a twin pump supply ..."
I understand that I cannot pump off the mains
 
What you are suggesting is, I think, essentially a break tank and a pump.
I don't see why you can't do this, but you can only pump the cold into the boiler. As its a combi, the increased inlet pressure will result in increased hot water out pressure. However, a few things to be aware of: (in a bit of a random order)
1. You will become dependent on the pump for all water in the property. If it breaks down you will have a problem, and might want to consider twin pumps, with one to take over from the other.
2. Power cut = no water.
3. You'd need to be careful the pump couldn't exceed the boiler's maximum input pressure. Even consider a pressure relief valve to outside.
4. Your boiler will only be capable of raising the temperature by (say) 35 degrees at its maximum flow rate. If this flow rate is 12 or 14 litres per minute, that's the best flow of hot water you'll ever get from it. Whether the hassle of installing tank and pumps is worth it only you can decide.
5. Wherever the tank is situated it will need an overflow (warning) pipe to the outside, which can be difficult in flats. Otherwise, if the float valve fails, you'll have a mains pressure flood inside the property.
6. You'll need to size the tank to provide a sufficient supply of water for general use. You can't have it running dry or you'll damage the pump(s)
 
You can buy a Homeboost pump and install that directly on your mains, it will give you enough flow (12L/min @ > 1bar - max you are allowed to pump the mains directly) and pressure for most combi's to cope with.

Before you ask, it works in a different way to a pumped stored water supply, it idles with the mains and then boosts when it drops below the max 12L/min. Combi's aren't designed to run from a pumped water store with that type of regenerative pump, it's down to how it delivers the water and you'd have nothing but issues.
 
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