Low pressure on shower

[BILLDIYNOT]

Hello. I have a 4 year old Vaillant combi boiler, serviced annually (last service July 2025). 4 bed dormer with 2 en suite showers and a separate bathroom shower, all off the mains water. There is only my wife and I living at the property. We had a guest, using the other en suite shower, from July to September, but he has now moved to his new home. Since around beginning of October, the hot water pressure in the main bedroom (downstairs) en suite shower has been slowly reducing. It comes out of the overhead fixed shower head very slowly when turned on and the flow increases after about 2 minutes to something that can be used, i.e. more than a trickle and hot (ish). I have bled all of the rads and also turned the stop valve off, (with the boiler off) and opened all of the water outlets, then turned the main stop valve back on and closed all of the taps, one at a time after any spluttering ended, where applicable. Neither of these actions, taken separately, made any difference. The hot water pressure out of other taps around the house is a little lower but not as noticeably as the main en suite fixed shower head. I also took the fixed shower head off to give it a thorough clean in case there was any limescale build up in the shower head nozzles. No difference. The main en suite shower also has a hand held shower head, which is, of course, on the same pipework as the fixed head. The pressure out of this also seems reduced. The cold water does not seem affected. I also increased the water pressure in the boiler to 1.8 bar from 1.5, but this has made no difference either. Your professional advice/suggestions to the basic cause and the remedy would be greatly appreciated.

 

[Johntheo5]

You could turn the shower temperature setting to maximum and the combi DHW temperature setting to minimum, say around 35C?, and see if the flowrate is "normal", at least that might show that the flowrate from the combi and through the shower is OK.

 

[Madrab]

No need to change the pressure on the boiler, this has nothing to do with water pressure, that's just the CH system pressure. The rads and the central heating in general, if it's working ok, will have nothing to do with the HW so no need to change anything there.

The key here is to see if the water pressure itself has changed, you mention that the cold water pressure is the same? If so then it's just the HW system that's affected. That circuit is from the cold mains into the boiler, through and out into the HW distribution pipework and out to the outlets.

From the behaviour of the main en suite shower, I'd be looking at the shower valve itself as a starting point and working backwards to the boiler. A pressure gauge would be handy here too - test the cold mains pressure and flow and then compare that to the hot and see where it varies.