Moving from vented to unvented cylinder

[mobile73]

Hi, we are thinking of moving from a vented cylinder to an unvented model. The reason for this is that the pressure in our house is extremely low (not the mains pressure which is > 3 bar I believe) and this has for many years been boosted by a pump. The pump has broken down (goes off the whole time) and is also extremely noisy so am looking at this as an upgrade rather than just replace the pump. I have been quoted approximately £2,800 + VAT (in London) to remove old cylinder, tank etc. and relocate unvented in loft. This includes pressurising the existing heat system.

Will the unvented system give as much pressure / output as the pump did?

Does that sound reasonable? This is a G3 plumber who I have used on other jobs so trust but wanted to understand if that is around the right cost. He said would be probably a Telford or similar tank. Thanks

 

[Johntheo5]

If you are hoping to use the mains to feed the UV cylinder then you need to check the dynamic flow, open a cold tap, maybe a outside tap and measure the flowrate, ideally you require a pressure gauge on the end of another cold tap to see what the (dynamic) pressure is, you will also have to allow 0.5bar for the loft elevation.

 

[mobile73]

If you are hoping to use the mains to feed the UV cylinder then you need to check the dynamic flow, open a cold tap, maybe a outside tap and measure the flowrate, ideally you require a pressure gauge on the end of another cold tap to see what the (dynamic) pressure is, you will also have to allow 0.5bar for the loft elevation.

Thanks - so does putting it in the loft reduce the pressure? Does the price quoted sound sensible for this kind of job (I know an impossible question to answer!)

 

[Johntheo5]

In the loft may not have a huge huge effect depending on points of usage, so maybe disregard., can't comment on the quote.

 

[Madrab]

It will lose as much pressure as the highest outlet.

A Dynamic pressure and flow test is key, that and knowing what the output of the pump is. Test pressure at a full flow tap closest to the mains (outside tap is the best) whist that tap is open, run 2 other close taps and check the 3 readings. The run say the sink and do a flow test at the outside tap to check dynamic flow.

 

[fixitflav]

This includes pressurising the existing heat system.

That's not essential. The primary circuit (through the HW cylinder coil) can be left as open vented, if you prefer. That should be cheaper, as the kit is already there, just a straight swap of the cylinders, and pressurised would need another expansion vessel. If it's an oldish place, pressurising might give a risk of leaks on the rad circuit.