Pump Problem

[adders21]

I think this will be a difficult one to answer but here it goes.

Previous owners in our house had an extension which added an ensuit.

In the ensuit there is a toilet, sink and shower.
The shower and the sink are both supplied via two pumps. The sink has mains pressure cold water and a pump for the hot. The shower has both hot and cold supplied via a pump. Both the hot and cold water pipes run up into the loft and then down into the ensuit. The ensuit is on the 1st floor as is the hot water tank.

My problem is that when the shower is running, if you try and run the hot tap in the sink it runs dry. To then get the hot water flowing I have to suck on the hot tap. This can take any where from ten tries to fifty.

Attached are pictures of the pumps from different angles. The pump for the sink is behind the shower pump.

Is there an easier way to get the hot water flowing again into the sink?

Is there a way to stop this happening full stop?

Thank you for reading.

View media item 43713 View media item 43712

 

[HERTS P&D]

Fit a 2 bar negative head pump for the shower and connect it to the basin also, that way you would only need one pump.


Andy

 

[Agile]

Perhaps you have not explained it cleary?

Why do you need to use the sink at the same time as the shower?

 

[4xpaws]

Clearly explained. It will be down to where the pump installers have tee'd into the hot water supply pipework. Take some photos of where the pipework for the HW for the 2 pumps are tee'd from. Should be around the vicinity of the hot water cylinder, but the given you've got problems with the single pump I would guess that one's higher up.

You don't need a negative head pump. You would fit one of these if the shower head was above the base of the cold water cistern supplying the hot water cylinder. Your shower's working fine. Wouldn't also go for a larger pump unless the rest of your system can keep up with the larger pump demands.

Look at fitting the hot and cold to the basin on the same pump as the shower. Although 'shower' pumps are designed to be pumping hot & cold together. With your basin you may want eg. just cold, in which case the pump's thrashing the hot as its got no where to pump it to. An alternative is to sort out where the pump(s) don't conform to manufacturer's installation spec. and correct.

I guess you've got a monobloc mixer on the basin.

 

[adders21]

Thank you for the reply guys.
Here is a picture of the hot water tank showing where the hot water is tee'd from.
I have ringed the tee in red, it is the copper pipe which then becomes the plastic pipe going up into the loft. It's about 70 cm from the floor. The pumps are lower than the tee as they are placed on the floor. The plastic pipe runs up into the loft, across the back of the house and then down into the ensuit. At some point here it splits to feed the two pumps.
The yellow dashed line shows where the hot water feed comes from the tank.
View media item 43829
Yes, we have a monobloc mixer on the basin.

 

[4xpaws]

The hot water (HW) pipework from the cylinder is only suitable for supplying one pump. In a fight the shower pumps got more pull than the basin pump. When the shower pumps running and you then run the basin HW, the shower pump pulls the HW from the pipework supplying the basin pump so it runs dry. Then you get an air lock so it wont re-prime once the showers switched off.

Monobloc mixers are typically designed for balanced high pressure hot & cold supplies. The monobloc was probably initially installed with mains cold and gravity HW and didn’t perform. The basin pump was then fitted as a bodge to give the HW some ummph. They’ve then bodged this pump into the existing dedicated hot supply to the shower pump to save on installation time & materials and/or were clueless.

Its hard to tell from pic but it looks like the grey plastic pipe from the cylinder is 22mm probably up to where the 2 pumps tee?

The 'easiest' options are:
-Remove basin pump and plumb hot and cold feeds from shower pump to basin. Though not good for twin pumps as mentioned previously.

- Remove basin pump, plumb basin HW into gravity HW and replace monobloc with 'dual flow' tap. - ie. HW and CW don’t mix until they leave the spout. Not a vast range to choose from.

-Remove basin pump pipework tee’d in shower HW pump pipework. Tee basin pump HW in pipework below the shower tee you’ve circled. Or keep the existing pipework coming from cylinder to supply the basin pump and run a new hot supply for shower pump from cylinder using an Essex flange.

 

[adders21]

Thank you for the advice 4xpaws.

The pipe from the cylinder is a 15mm pipe. So I guess that doesn't help.

As an experiment I will try removing the basin pump. It's quite easy to adjust the pipe work to bypass it.

If that doesn't work I think your last idea is the best and give them both dedicated feeds.

 

[4xpaws]

Remove the basin pump and it should show you why the pump was fitted in the first place eg.: Poor gravity HW flow on its own and trying to get a satisfactory HW CW mix is exacting. In most mixing positions the higher pressure cold will just be felt coming out the spout, meanwhile the HW is being pushed in reverse by the dominant cold all the way back up its pipe.