Taps/Shower Losing Pressure (Sealed System)

[b0ng0]

I've just moved into a new build house that has a sealed system installed. Pump broke after two weeks but was replaced (Grundfos, can't remember the model at the moment).

Everything was fine initially, but recently the taps and showers in the house have visibly lost throughput - water still comes out but about half the rate as before. This is for both hot, cold and mixed water.

Sometimes if I leave the tap running for about 30-60s, the flow increases back to what it used to be. However, in the shower it seems to come on strong but then die off. Also, if I start altering the thermostat on the shower the water starts "pulsing" as it comes out - enough to cause the shower hose to twitch like an itchy snake.

The pressure reading on the system sits around 1.5 bar when I last checked, which seems normal (I was told between 1-2 bar should be fine, otherwise top it up).

I'll get on the builder's case, but was hoping to get some help diagnosing the issue myself to make sure they don't just put a plaster on the issue rather than fix the cause.

 

[DP]

1.5 most likely boiler pressure, nothing to do with hot water delivery to taps

Is the hot water erratic at say the kitchen tap?

What make is the boiler and do you have a separate cylinder?

 

[b0ng0]

Okay, here is where my ignorance shines through - the 1.5 bar I'm referring to is a small pressure gauge close to the pressurized cylinder near the hot water tank - so I had assumed this was the pressure applied to the whole HW system.

The hot water does not have the same pulsing as the shower does, but it comes on strong for a few seconds then the pressure appears to die off.

The boiler is a Potterton PROMAX Condensing boiler (i.e. not a combi). There is a very large hot water cylinder on the ground floor, in the same cupboard as the pressure vessel and pump. They are about 1m away from the boiler itself.

 

[Madrab]

Couple of pictures will help but it sounds like you have a sealed CH system and you are reading the system's pressure gauge at the expansion vessel. As DP mentions this pressure is only for the radiators and the circuit running to the hot water cylinder coil to heat the water, it has no relation to the pressure/flow of the water at the taps.
Unless you have an unvented HW cylinder then your hot water is fed from a cistern in your loft to the hot water cylinder and some of the cold (kitchen usually) will be under mains pressure with any mixer outlets (taps/shower), if plumbed as a balanced supply, being fed from the cold water cistern.

First thing to get checked is the static and dynamic pressure of the cold mains and the flow rates.

 

[b0ng0]

Madrab, that's correct it's a sealed CH system. I wasn't aware that the expansion vessel only supplied pressure to the rads.

Is there any way for an amateur like myself to check the pressures of the cold mains or is that something a bit more technical?

 

[Madrab]

Nope, pretty straightforward though you will need a pressure gauge that will fit onto say a washing machine outlet or bib tap.

Flow is easy, get a bucket, mains cold tap full on and time for a minute, then measure how much water there is in the bucket = Litres per min.

Rob

 

[b0ng0]

Thanks, will give this a shot. They are still building new houses around the area so maybe something has happened with the mains supply to the area.

 

[Madrab]

The pulsing of the shower could be down to the thermostat reacting to the cold pressure fluctuating.

It certainly could be affected by other houses joining the mains and coming on line and may take time to settle once all the connections have been made.

 

[b0ng0]

Yeah, it seems to be getting worse as each day passes actually (by worse, I mean the cold water pressure seems to be dropping). The kitchen sink cold water tap however seems to get full pressure, but all the upstairs bathroom taps are almost a trickle now.

 

[Madrab]

Yup, get it tested, or get your supplier in to check, it is their service to you that is being affected after all.

 

[b0ng0]

Just had the plumber in, apparently there was some construction debris in the pipe just under the kitchen sink (where I assume the mains comes in). Changed it out and it seems that the pressure is restored but does make me wonder if there's any more floating around the system...

 

[Madrab]

Yup, the more work on the mains there is then the more likely debris can get in, nothing really to be done unfortunately. I would notify the supplier though.