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Low pressure water only in bath

  flycatcher1 22:38 05 Jun 2014

A friend has had a combi system fitted in his bungalow since then the water pressure is the bath is very low. All other taps over wash basins and the sink are fine. The problem has only happened post combi. His plumber says that nothing can be done - I doubt this and would appreciate any ideas on the subject.

  Forum Editor 22:53 05 Jun 2014

It's important to recognise the difference between pressure and flow rate. Cold water will be delivered to the bath directly from the mains, so unless there is an intermediate pressure reducing valve the pressure will that of the mains supply. The flow rate will be governed by the supply pipe diameter.

Hot water will of course be delivered via the Combi boiler, so flow rate will be reduced as the water has to pass through a plate heat exchanger.

  bumpkin 23:11 05 Jun 2014

With a combi the pressure to all taps will be the same. The flow however may appear to be slower from a larger tap. This is normal.

  flycatcher1 23:16 05 Jun 2014

Thanks for the prompt replies. The flow of hot water is only slow over the bath, the washbasin in the bathroom is OK. He says that it takes "for ever" to run enough hot water to have a bath.

For one reason and another I have been elected to sort this problem out and I need some background before I employ a plumber of my own choosing.

  bumpkin 23:27 05 Jun 2014

The flow rate from the hot and cold should be about same (without the technicalities) If the flow from the hot is as little as you say then it could be obstructed by something in the pipework or tap.

  bumpkin 23:32 05 Jun 2014

It is an easy thing to test, turn on the cold only and see how long it takes to fill for example a 5ltr container, repeat with the hot water. If there is a big difference then you have a problem.

  bumpkin 23:50 05 Jun 2014

rdave, sorry to disagree with you on this occasion but there is no legally set temperature.

  spuds 00:03 06 Jun 2014

I recently had a combi boiler fitted, as some of you may recall. Since then Worcester Bosch have sent an engineer to do a 'performance test' on the boiler. Worcester Bosch set their boiler regulated temperature at 50 degrees.

The W/B engineer suggested that any problems with hot water flow or temperature, a 2 minute open tap free run of water should locate any issues, because by that time the system should have stabalised itself?.

Not sure if that's the answer you are seeking!.

  carver 07:59 06 Jun 2014

It depends on the size of the boiler and it's ability to heat the water, it may appear to be flowing better out of a sink or kitchen tap but that is only because of the diameter of the outlet.

If the boiler output is too small it can only heat so much cold water to a set temperature over a set time and no amount of messing with it will increase the flow rate.

His plumber looks like he has fitted too small a capacity boiler for your friends needs.

  Forum Editor 09:08 06 Jun 2014

carver's response is correct.

The boiler will only deliver as much hot water as can pass through the plate heat exchanger and be heated to the preset temperature.

When you open a bath tap the flow rate will reflect that fact. Make sure your friend has not set too high a temperature on the Domestic Hot Water control on the boiler panel - people often have this set too high, and have to add cold water to the bath to get the temperaure back down to a comfort level.

Reducing the temperature setting will increase the flow rate, but not by a huge amount.

The boiler will have a Kilowatt rating. Try to find this out, and then post back with that information, plus the number of hot taps and radiators in the house.

  bumpkin 10:09 06 Jun 2014

Checking the flow rate from the hot tap with the boiler off will give further clues as to the cause.

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