Please help me understand my problem and what I can do about it!!

[Phil12345]

Right...

I have a potterton ff50 and a 90l cylinder with tanks in loft. Hot water flow/pressure coming out the taps is rubbish.

Want to have a new bathroom with thermostatic mixer shower but flow is far too low currently.

Been recommended an unvented cylinder but don't want to accommodate a cylinder and worried my budget will all be spent on that only for my boiler to need replacing at some point. The plumber who recommended that measured 18l/min and 3bar pressure at outside tap. As well as a 22mm pipe straight to cylinder from stop tap.

Then we decided that a combi might suit us better convenience wise.

Another plumber measured 12l/min and 3 bar??? He put a 1 bar restrictor on and it went down to 10ish.

We have blue mdpe pipe coming into house and it then turns into 15mm stop tap and pipes after that.

What the hell do I need to do to ensure I get a really good shower on a 150mm square shower head....

Obviously I'm no pro so I've no doubt left out critical info but please do ask away!

 

[flameport]

Vented cylinder with a pump. Unfortunately, a 90 litre cylinder such as the one you have now won't last long with a large shower head.

Unvented is unlikely with your water pressure/flow, depending on which plumber you believe and whether the pressure and flow were measured together or separately. Something else to consider is that pressure can and often does vary depending on the time of day, so both plumbers could be correct. Or wrong.

A combi can be used with a normal shower head but performance will be poor with a large one.

 

[Phil12345]

Thank you so much flame port. I was pretty keen to get rid of all the tanks and stuff but guess that's not possible is it?

How big a job is it to upgrade internal pipe work as I guess that is where the flow restriction is coming from?

Would you just replace my vented tank for a bigger one and add a pump then?

 

[Phil12345]

What I want is s bloody good flow coming out of a large shower head.

What is the simplest way to achieve that?

 

[it's not that hard]

has the hot water pressure always been low ?

 

[bernardgreen]

Unless you put in a combi that can heat the water for the shower to the flow and temperature you want for the shower you will have to have some form of heat storage. The combi option is the simplest to install ( assuming minimum flow rate and pressures are as required by the combi ). The down side to that simple solution ( much favoured by some installers ) is that the combi will have to be 30 or more kWatt to be able to supply the shower and then modulate down to maybe less than 3 kWatt when only heating the house. Will the comb be efficient at those two very different level of heat output. With a heat store and heat only boiler the boiler can be running at its most efficient setting while heating the water in the cylinder.

How to heat the mains pressure water to the shower with heat from the heat store ? . It could be an un-vented cylinder supplying water to shower and taps. The water is under pressure and thus the flow at shower and taps is also under pressure. Good for the shower but can lead to the water in basins coming out of the tap too fast. Major disadvantage with an un-vented cylinder is the need for a G3 qualified technician to install and maintain the cylinder. Annual checks on the safety devices are necessary and require a G3 qualified technician.

Water in a vented ( unpressurised ) cylinder can be pumped via a heat exchanger to heat mains pressure water that feeds the shower. Other taps in basins and bath are supplied with hot water direct from the cylinder so are not under pressure. Compact heat exchangers such as plate exchanger can and often do get clogged up with lime scale and have to be internally cleaned or replaced. Also requires a bronze ( not cast iron ) pump to preserve the quality of the water in the cylinder that will be going to the taps at some time

A passive heat exchanger can be a second coil in the top of the vented cylinder ( or wrapped around the outside of the cylinder ) through which mains pressure water is fed to the shower. It does require a non standard cylinder but the extra cost of the cylinder is about the same as the cost of the pump and plate exchanger that are not required.

"professionals" on the forum may disagree with the last paragraph. It works for me and has done so for the past 5 years.

 

[Dan Robinson]

Not so much disagree, but think you a bit foolish. Transposing one set of disadvantages for another without explaining.

Plate heat exchangers - lime scale? Did Google teach you that?

 

[Phil12345]

We've been here just over a year as its not changed in that time. We use the electric shower every day as a main which is not great!

I really wanted to lose the cylinder and tanks for the space if I could but it may not be possible.

Is it a case of swapping the 15mm pipe in from the front door stop tap or is that pointless?

Trying to increase flow into house to ensure a good flow for a combi that can cope with producing enough hot water for a good shower with a large head (not crazy large but about 15cm sq)

I really appreciate the comments and effort to help me!

In our last house we had a combi and the exact shower head we want and it was absolutely brill. Appreciate that was a different house but to the untrained amateur it's frustrating not to know what to do to get that solution to work!

 

[Dan Robinson]

How big is the house? Not very I guess.

 

[muggles]

A combi might suit you, and would certainly give you better performance than your electric shower, but it's quite possible that both the guys who measured your water flow and pressure are correct and that you are suffering from large variations according to the time of day. If that's the case then you're going to suffer that variation in the performance of your shower if you go for a combi, and unless you couple your unvented cylinder to an accumulator you'll also see the same variation in the performance of an unvented cylinder.

Where in the country are you?

 

[bernardgreen]

Plate heat exchangers - lime scale? Did Google teach you that?

NO

The company I bought one from told me, it is still on the shelf, I opted from a different method. ( hasn't a RGI on this forum mentioned that plate heat exchanges can get limescale deposits inside them. )

 

[Phil12345]

Hiya

It's a 3 bed house with 1 family bathroom and 1 little ensuite size shower room with the electric shower in.
It's me, the Mrs and our 5 year old son.

 

[it's not that hard]

Just an idea,I had a customer who wanted a combi fitted in a low water pressure area,I said have a new water main moled into your house (cost £250 15 years ago) and connected the 2 mains together which gave enough pressure to have a combi,I advised her to change the bath mixer/shower taps as they were the telephone type which has a big spout and the hot water pressure was lost,the same principal as your big shower head.

 

[it's not that hard]

Not so much disagree, but think you a bit foolish. Transposing one set of disadvantages for another without explaining.

Plate heat exchangers - lime scale? Did Google teach you that?

LOL, whats wrong with Bernards answer,I'm sure that it is crystal clear to the op,just pop down to the van to get toolbox,a bit of tinkering about, job done

 

[Dan Robinson]

Plate heat exchangers - if specced correctly, will flex and break off the scale. Unless in a crazy hard water area in which case treatment should be in place anyway.

Having two water supplies will do nothing for the pressure. It will increase the flow rate.


I do agree with Bernard that combi's are a nightmare in these situations, although Vokera and Viessmann are making great strides in Turndown ratios. However they are a compromise. My default solution on this system (as described) would be a 180 litre unvented cylinder sitting under a 15kW or 18kW system boiler on hot water priority.

The 15mm copper should be changed for 22mm all the way to the cylinder location and the cold for the house drawn off the balanced outlet of the cylinder control group. If the upgraded pipe is not going to work, replace the cold water cistern with the aforementioned accumulator and then put an unvented cylinder in. Maintenance would add an hour per year, but an engineer with G3 unvented is hardly going to cost anymore than one with Gas Safe registration. Christ, it only takes 15 minutes to renew the certification when taken with the other exams.

Of course you can keep your cisterns in the loft and have noisy mechanical pumps.