Plumbing Query

[Old_Geezer]

In a bungalow the hot feed to both kitchen and bathroom is not powerful (to say the least). I went into the loft to try to measure/estimate distances. I reckon the bottom of the cold header tank is 2.5" above the top of the hot water cylinder; and although I have to guess the thickness of the kitchen ceiling I reckon the bottom of the hot water cylinder must be about 63.5" above the taps.

I tried to find out if this was ok but there seems to be some rule about not having that information on the internet. The best I could find was, suggestions of 0" to 3" for the former distance, and 80" for the latter. Does this sound correct, and could the inability to increase the fall be the cause of the issue ?

(I did try to unblock any potential airlocks first. Messy business on combination taps :-( which seemed to help slightly (may have been my imagination) but has not solved anything.)

Cheers.

[Garaman]

Work on about 0.1 bar per metre drop, OG, so you have about 0.2 bar which isn't very good. Ideally you would want 0.4 for a reasonable pressure. You options are to install a pump, or switch to a high pressure combi boiler and do away with the hot tank.

[Old_Geezer]

Thanks. She won't be pleased to hear that. The first probably needs mains power in the loft and I'm unsure if there's presently more than a lighting circuit there at the moment, and the other sounds expensive. No obvious place to put a combi either. Some websites suggested a vent free whatever, but that also sounded expensive.

(Loft isn't exactly pleasant, loads of fibreglass insulation exposed everywhere, and relatively little boarded. Plus nigh impossible to get the other side of the tanks, without going through the ceiling that is.)

[Garaman]

I had less header than that in a flat in London years ago. It was only the shower that really bothered me so I put a pump on that pipework only and left the rest as was.

[bhg481]

Lighting circuit is adequate for a shower-pump, which is the sort of thing you could use. They cost around £100 and switch themselves on/off when the water starts/stops.

[Old_Geezer]

It's not really the shower that's of concern. I've not used the shower there but it's an instantaneous electric one and I believe it's ok. The issue is the weak hot water flows at the kitchen sink and bathroom basin. But if a pump is installed in the loft prior to where the pipe splits into two, maybe that can run off the lighting within the regs ?

[bhg481]

O-G - that's what I meant. You can use a shower pump to increase the flow at your taps. A shower pump is fitted between the header tank and the taps and can take its power from the lighting circuit because an earth will be available and the power consumption is low enough. Shower pumps have a flow sensor in them so that when you turn on a tap and the water begins to dribble through, the sensor is triggered and switches on the pump. When you turn-off the tap the flow stops and the sensor switches-off the pump.

[Old_Geezer]

Sounds like you are both in agreement. What size pump ? Are we looking at 2 bar because it needs an additional 2, or 4 bar because it needs a total of 4 ?

[The Builder]

For my 2 cents' worth, OG ...
I agree with everything said so far. Selecting a pump is critical. A too powerful pump can cause a problem if the gravity feed from the tank is unable to keep up with the pump. In extreme cases, the cistern in the roof could empty before the incoming mains feed is able to replenish the amount of water.

I have seen this happen with a bath, which needs a lot of water. Then you get air drawn in, and thus airlocks.

Raising the roof tank can help a great deal, but it's a biggish job, and you may not have sufficient headroom anyway.

A good start is to look at the hot pipework. Ideally, a 22mm supply would be taken from the cylinder directly to the kitchen tap. Remember, your problem is with flow rate ... not necessarily pressure. Also 22mm to the bathroom would help. All too often, 22mm from the cylinder is immediately split into two 15mm supplies which run to kitchen and bathroom. 15mm can give flow rate problems.

Also, check that you don't have any isolation valves in the pipe runs. These have a tiny aperture that severely restricts flow. The other common problem is with modern posh taps. Some work at a low pressure... many don't. The old type full-flow type with handwheels tend not to have this concern.

[bhg481]

I replaced my shower pump a few months ago and seem to remember paying about £100. Looking at Wickes and Screwfix that would have been 1.5 bar. As pumps seem to cost about £100 per bar and mine provides ample pressure for a shower in an upstairs bathroom with the header tank sitting on the joists, I would go for that size. £100 for a Wickes own brand, £130 for a Salamander from Screwfix.

[Garaman]

Your pressure presently is about 0.2 bar, OG, not 2, and the header you have won't make any difference to the pressure from the pump. It is really a question of how much pressure you want. As it is clear that you aren't concerned with a power shower, 1.5 - 2 bar would be more than sufficient.

Builder is spot on as usual.

[Garaman]

Sorry, OG, I should have been clearer, by 'power shower' I mean one with extreme water flow (like ours which has a massive overhead rose, or one with side jets), 1-5 to 2 would cover most normal showers.

[Old_Geezer]

Thanks all.

Replacing the piping all the way sounds like a good idea but quite a job. IIRC it is 15 mm all the way, or as near as dammit. May leave option that until the pump idea fails to solve the issue.

I'll look into the pump thing and see how it goes. Any particular brand that's a good balance between quality and price ?

[Garaman]

I can't offer advice on quality/price I am afraid. I have only used Stuart Turner who make really top quality pumps, and it is 25 years or so since I installed one.

[bhg481]

After reading reviews I opted for the Salamander from Screwfix when I replaced mine. It's dearer than the Wickes but got better reviews.

[Old_Geezer]

Cheers again.

[Old_Geezer]

Hmm... Wasn't quite as I thought. Wasn't two pipes from the cylinder, one to kitchen, one to bathroom after all. When I checked it was a 15mm cold riser and 22mm hot fall into the kitchen. Can only assume bathroom tees off the kitchen one behind the base units somewhere. Pumps are complex aren't they. Need to ensure 22mm fitting, but these single or double impellers and some aren't for gravity feed, and some are shower, some home booster. How complex can a pump be ?

[Garaman]

I think the home boosters are to boost the mains pressure when that is low, which isn’t your situation from what you have described.

Whether you want single or double depends whether you want to pump just hot, or both hot and cold. These pumps are mainly used for showers where it is important to have equal pressure in hot and cold otherwise it is a difficult to control the temperature, hence for a shower it is best to use a double pump. It used to be common in buildings (don’t know if it still is) to have cold mains at the kitchen tap but have the cold in bathroom from the cold tank then it is the same pressure at the hot water in the bathroom so with that sort of arrangement it is usually not difficult to install a double to boost the bathroom.

However, you didn’t mention the pressure in the cold taps being low, so I am assuming that your bathroom cold is also at mains pressure. You also mentioned an electric shower which I assume is connected to the cold water at mains pressure. If that is true, and you are happy to leave the shower as is, and only want to boost the hot, then I would say that you just need a single pump on the 20mm hot water down pipe. That would boost your hot water pressure to kitchen and bathroom taps.

Whether you need a positive or negative pump depends where you intend to install it. A positive head pump would need a decent header distance (say 1 metre) between the pump and the bottom of the cold tank – gravity starts a positive pump. If you intend to install the pump higher so that it isn’t more than 1m below the tank you would need a negative pump.

[Old_Geezer]

The only sensible place to cut in and insert a pump would be in the loft, perhaps next to the cylinder, so I don't see my being able to get a great drop. 0" from cylinder, but about 37.5" from the cold header. So borderline ? So what starts a negative pump ? Surely a little flow starts both up ?

[Old_Geezer]

Centrifugal/regenerative ?

[Garaman]

Some work by pressure, OG, so when a tap is opened they sense the change in pressure. Some pumps are either positive or negative - not sure if they use just pressure or both flow and pressure. The main thing is to make sure you get one suitable for the location you are going to install it.