This post is inspired by a customer who has limited space to fit the SP21S double pressure boost and has just now asked if can he put a a pump either side of the Combination Boiler. The question opens up the whole subject of when, where, and why you can boost a hot water supply from a Combination Boiler.
Boosting Before The Combi Boiler
A Combi Boiler will only fire up if you have a minimum of one bar pressure on the cold.
A Combi Boiler will turn itself off if the pressure drops when in use if the incoming pressure falls below 1 bar.
A ShowerPowerBooster will solve this problem and this will also boost the hot water pressure after the Combi. If neither applies to you then the problem is not because of low pressure on the inlet side and further boosting will have little effect.
Boosting After The Combi Boiler
Boosting the pressure after the Combi Boiler will not increase the pressure before the Combi Boiler to stop it dropping out but it will always boost the pressure after the Combi Boiler.
If you have 10 metres head before the boiler and the hot water pressure and flows are poor, even on short pipe runs, then it could well be the boiler itself thats the problem. If you have long pipe runs and/or lots of air locks, the ShowerPowerBooster will always boost the pressure.
The ShowerPowerBooster is most effective when fitted on a single feed to a shower our tap but is equally effective when that shower or tap is the only tap and shower in use. The boost given by a ShowerPowerBooster is reduced if more taps and showers are in use at the same time and the device will deactivate the pump when 3 taps or showers are in use so if you have 3 problem showers you need 3 pumps on 3 separate pipes.
One or Two Pumps?
The fitting of a single SP2B fully automatic pump will normally suffice but because there is little risk of creating an unbalanced hot/cold pressure upstream of a mixer tap or shower we recommend a double pressure boost by fitting a SP21S.