customer wants a pump fitted on the hot water so all hw outlets are pumped.
The system has mains cold water throughout and gravity hot water with gravity secondary return.
I'm not too sure how the secondary return part of the system will react with a pump being fitted.
Has anyone done similar ?
If I ever encounter a booster pump on a plumbing system it tells me there is a problem. The problem is that the plumbing system is not fit for purpose - root analysis.
Fitting a booster pump just treats a symptom. Booster Pumps on plumbing systems always cause problems.
The key problem you will have here is 'cavitation'. Given that the primaries are gravity, it tells me there will be no or little control over hot water temperature, this means that in winter the boiler stat will be set on 80-85 degrees plus in order to get the rads hot (which results in the gravity primaries providing hot water at the same temperature).
The very nature of a booster pump causes positive pressure on one side (1-3 bar) and negative pressure on the inlet side. The negative pressure is important to consider, because it causes water to boil at lower temperatures, producing steam. The pump cannot prime if it is full of vapour and this causes cavitation or water boiling at lower temperatures - there are affects of this, which are detrimental to booster pumps.
The consequences are usually noise and early failure of pump.
In addition you may encounter taps, mixers and shower problems because the core of the existing system is designed for low pressure. Add to this micro leaks on the inlet side of the secondary pump, and you have a nest of vipers.
Modern pumps are particularly sensitive to temperature, and this must be maintained in the hot-water storage at 60-65 degrees c, which is impossible with gravity primaries in winter.
