Plumbing (House) Advice Needed – Hot Water System

[Ayjay]

Any plumbers out there please?

Ever since we moved into this house the hot water system has had low pressure to the hot water taps. We have a water tank in the loft feeding a 120L electric immersion cylinder just below it in a cupboard on the second floor and that provides hot water to the shower (via a pump which gives a good flow) and sinks in the bathroom, downstairs toilet and kitchen which all suffer from poor flow on the hot side but it’s the kitchen tap that’s the real problem (in terms of ‘pipework’ the kitchen is furthest way from the cylinder)

A few years ago, we had a new copper cylinder fitted which is when the problem below started. Since then we have had three different mixer taps (all supposedly designed for low pressure systems). The latest is a cheapo (IIRC £80 Ikea) but the previous two were more expensive from Franke and Grohe and all of them had the same issue. As said above, the flow from the hot side is poor, so poor that sometimes when we turn it on, no hot water comes out. At other times, it takes a couple of seconds to start but more often starts straight away. On the occasions when it doesn’t start at all, turning the downstairs toilet tap on and off gets it going.

I’ve been told that installing an ‘unvented hot water cylinder’ is the answer to the problem and have done a bit of research on line which seems to support that but any advice from people on here would also be much appreciated. As far as I can see, the two main drawbacks are:

1. How much hot water the things can get through (as it comes out at mains pressure) but a larger cylinder might sort that out.
2. I have also read that they should be inspected annually by a suitably qualified plumber which would be an ongoing cost but might also give problems when you;ve got to find somebody to actually do it.

Any advice on this would be much appreciated. Nowadays, I’ve actually got a plumber who I trust who can do the work but I always like to be armed with a like bit of knowledge before I talk to a tradesman.

 

[Dannyb6467]

Hi bud, I have 2 invented cylinders feeding a 9 bed house over 3 floors and the water pressure at the furthest tap away is excellent, it's basically the same as the pressure at the nearest hot tap....which in turn is the same as the cold taps. As for using more hot water....you're correct, hot water is supplied at mains pressure but flow is as much or as little as you open the taps...it uses no more water than your immersion heater does currently. I'm no plumber but it seemes strange that sometimes you don't get any hot water....air locking somewhere??
My unvented cylinders are checked every year when we have the boiler serviced.

 

[T6 Syd]

Hi, not a plumber but looked into this when renovating our house. If going for an unvented cylinder you do need a plumber with the relevant qualifications (G3 I think), and yes it should be checked over every year by such a plumber, as should your gas boiler by a Gas Safe engineer. The mains pressure hot water from an unvented cylinder should improve things and may or may not negate the need for the pump on the shower. The existing pump may not be suitable for a mains pressure hot water supply and may need removing or changing anyway.

An alternative is an open vented thermal store with a plate heat exchanger for the mains domestic hot water provision. The hot water is heated as it is drawn off from the mains, not out of the tank of heated water. The tank of water is only a heat bank, hence it can be unvented. That system does not need any special plumbing qualifications and being open vented does not have to be checked annually. It will likely run a shower without the need for a pump. The downside is that it is a much more expensive system (but as you are on this forum that suggests that you are willing to pay a bit more for engineering/design and probably maintenance ).

However, your problem as described is perhaps more complex. Your water tank supplying the 'pressure' to your hot water taps is in the roof. Assuming you have a typical two storey house with the kitchen on the ground floor then the standing pressure available on the ground floor is the highest in the house, better than in a bathroom on the first floor. The pressure or head is related to the height of the level in the tank in the roof above the outlet point. If you are getting poor flow in the ground floor hot taps then it is the pressure drop (resistance) through the pipes that is a problem. Small pipes and or too many bends and perhaps valves throttling the flow. Maybe even a crushed pipe. If there is too much resistance in the pipes that may account for the intermittent inability of the opening of the kitchen tap to cause the water to overcome the resistance and start flowing - overcoming the inertia, in simple terms think about the effort required pushing a van to get it to move compared to the lesser effort to keep it moving. Opening a second tap opens up more outlet area, releases more pressure from the pipes at the taps giving a greater pressure difference between the tank and the outlets to overcome the inertia.

Changing to an unvented hot water tank will likely give you flow at the kitchen tap, but it will still be restricted from what it could be due to the pipework issues. However, changing the cylinder may be cheaper, including ongoing maintenance faff, than the cost and disturbance that may be required to trace and sort the pipework issues.

I went with an open vented heat store (heat bank), but what can I say, I also have a T6!

 

[Hilly64]

dependant on size of house ie how many bathrooms, en-suites etc and age of existing boiler you may find switching to a modern condensing combi boiler worth considering. They have their limitations however some of the options suggested may not be cheap and a new boiler could be a simpler cheaper more energy efficient option especially if existing boiler is old and end of life

 

[Stay Frosty]

We had to notify the local council when we had an unvented system as the stainless water cylinder has the potential to turn into a modest bomb if things go wrong.
Might be easier to fit a combi boiler and do away with the gravity system?
Bugger slow typist.

 

[T6Plumber]

Hi mate, I’ve DM’d my number if you want to have a chat & run over options

 

[Ayjay]

Thanks for all the quick responses and a big public thank you to @T6Plumber (Luke) for taking the time to talk me through it all this morning. I'll have another conversation with my local guy later this week but I think the unventilated system is the way to go. Thanks again for all the inputs.

 

[Stay Frosty]

Unvented as in 3 bar stainless steel pressurised hot water storage cylinder rather than old school header tank fed low pressure copper immersion heater type cylinder.