Pump for hot and cold water supply to bath

[AjayK46]

My existing supply to the bath has the cold coming straight from the cold water tank and the hot from the hot water tank heated by an immersion.

Having had a larger bath installed it will not fill quick enough from the hot so the water is getting cold even before you have got in.

I have been told that I need a pump both on the hot and cold water supply to the bath.

I already have a power shower which has an integral pump and the hot comes via a Surrey Flange on the hot tank and a separate outlet from the cold water tank well away from the stop cock valve.

I am told that the additional pump I need for the bath water supply should also have its own dedicated supply from the hot and cold. The cold is not a problem but with a Surrey Flange already fitted to the hot tank how do you provide an additional dedicated supply from that?

I'm not doing the work myself but I want to be prepared for what the plumber will need to do.

Any help appreciated.

[plumbbob]

There is no requirement to have balanced feeds to a bath in the same way there is to a shower so it is not necessary to pump both hot and cold supplies.

The easiest way to solve a poor bath cold fill is simply to change the feed from the header tank to the mains feed. The extra pressure will ensure a quick fill.

If you need to pump the hot supply it may be possible to link it to the same flange as the power shower. These flanges often supply two showers anyway.

IT might be worth looking at why the bath takes so long to fill with the existing arrangement. Low pressure systems have filled large baths successfully for decades so why is there a problem. What we see today is a shift to high pressure heating systems utilising Megaflow or combi boilers. This means suppliers can get away with selling taps with smaller bores that really are poor performers in a low pressure situation.

Low pressure systems must have 22mm feeds to the taps so if flexible tails are fitted these may be restricting the flow. Simply upgrading these may solve your problem.

[AjayK46]

Thank you for this information. The feeds to the bath hot and cold are 22mm. The bath is one of the "P" shaped ones so it does need quite a lot of water to fill.

If we go the route of a twin impeller pump is it therefore ok for the plumber to split the hot supply that comes off the Surrey Flange for the shower and just divert the existing cold supply for the bath via the pump? I only want the pump cutting in when either the hot or cold taps for the bath are turned on without interfering with anything else in the bathroom.

Cheers

[plumbbob]

You might be able to use the Surrey flange to feed the hot, but to be honest it wouldn't be the best idea probably. These flanges take the water further down from inside the tank so you don't actually draw the hottest water available. Also, if you are filling a shower bath, you need the maximum volume of water available and the fact it is taken part way down means you may run out of hot before the bath is full.

Next, you can't use a twin impeller pump to feed both the hot and cold to individual taps. These pumps are designed to supply water equally in a shower situation. In practice you may only be drawing off the hot side which would put undue strain on the pump because the cold is not flowing. It may result in the pump failing.

Also, the pump uses the flow of water to sense when to switch on. If one feed was off the pump may not run at all, or alternatively, it may keep switching on and off (hunting). It certainly wouldn't run correctly.

[AjayK46]

I'm rather confused. The pump that my plumber wants to fit is a Stuart Turner Monsoon brass bodied 1.5 bar twin impeller model 46506. It states on the box "Presurise your whole home, Bathrooms, Bath, Shower or tap"

In my case it is just for the bath which has a mixer tap. Are you saying that with the pump fitted if I only have the mixer tap on maximum hot that this could damage the pump because no water is running through the cold side?

[AjayK46]

Any further help would be appreciated.

Cheers

[plumbbob]

Sorry for the delay in response, it's the panic due the Christmas rush.

I can see from the installation instructions, the pump you mention is suitable for "full house" but doesn't mention any examples of how this might work only mentioning bath mixer taps.

For supplies where hot or cold may be called independently, we have always fitted individual pumps for each. Twin pumps are only used where the supplies are required to be balanced.

I have been trying to remember the last domestic installation that required a pumped cold, and I can't recall a single instance. in the last 20 years. Since the 80's all cold feeds are mains fed and with low pressure systems being phased out, this is even less likely to happen.

I can't understand why you would be willing to spend extra money buying a more expensive pump to boost the cold when the bath should be a at mains pressure anyway?

Call the Stuart Turner helpline and explain your intentions. They will be able to confirm the suitability and suggest the best model of pump.

Hope this helps.

[AjayK46]

Thank you for your further reply. First of all both the hot and the cold to my bath are from the relevant tanks and the flow on both is poor.

I have just spoken to the Stuart Turner technical help line and asked them this question.

"With the 46506 Twin Impeller pump if only the hot tap is opened and the cold therefore is not being used would this cause damage to the pump"

There reply is that the pump is perfectly designed to do this as it is two pumps in one casing run by one motor. If no water is required on the cold side then that side of the pump just "treads water" and is perfectly safe and will not cause damage.

Regards