Advice on System vs Combi with accumulator

[Robotman]

Hi,

I currently have a combi boiler which drops flow rate when a second tap is turned on. I'm also looking to add a second shower. The flow rate i have is 12 ltr per min and i cannot install a blue pipe because a i have a shared mains with the neighbour.

I have a couple questions:

If i place a system boiler with an unvented cylinder on the ground floor, would i have enough flow rate to service the 2 showers that are on floor 2. I dont want the flow rate to drop when both showers are on or when a 3rd outlet is on.

second question.

what would be the best solution: System boiler with unvented cyclinder or combi that has small storage unit (Valiant ecoTec + 938) with an accumulator to service the showers only?

Thanks in advance for all your advice and input

 

[oldbutnotdead]

12 l/min (if that's from the cold tap nearest the stopcock) is not enough to make an unvented cylinder work. You can dig a new supply pipe in, might cost a few quid but until you do so you will have poor flow and fluctuating pressure on the mains supply
If you don't want to dig a new main in, fit a vented cylinder 250ltr or so and a boost pump.

 

[Robotman]

12 l/min (if that's from the cold tap nearest the stopcock) is not enough to make an unvented cylinder work. You can dig a new supply pipe in, might cost a few quid but until you do so you will have poor flow and fluctuating pressure on the mains supply
If you don't want to dig a new main in, fit a vented cylinder 250ltr or so and a boost pump.

Thanks for your thoughts.

How about having a storage combi to serve the house and an accumulator to service the electric showers only. What are your thoughts on this solution?

 

[oldbutnotdead]

Thanks for your thoughts.

How about having a storage combi to serve the house and an accumulator to service the electric showers only. What are your thoughts on this solution?

You'll be throwing a lot of money to get an average outcome. Electric showers at their very best give a poor to average shower, storage combi doesn't solve your poor water supply. Sort the supply pipe out first (not sure on costings for a new connection to the main) then decide how best to proceed once you have decent flow and dynamic pressure.

 

[Robotman]

You'll be throwing a lot of money to get an average outcome. Electric showers at their very best give a poor to average shower, storage combi doesn't solve your poor water supply. Sort the supply pipe out first (not sure on costings for a new connection to the main) then decide how best to proceed once you have decent flow and dynamic pressure.

Thanks, I checked with the water board and it's going to cost upwards of £3000. I checked the pipe that coming into the mains and its a lead pipe.

Also had a plumber come in today. His suggestion was to go from mains to an accumulator with built in pump (Mainsboost Flomate MBF 300-1-15) then accumulator to a combi. However, he also suggested that in the long term better to get the mains upgraded to 25 or 32mm pipe.

 

[oldbutnotdead]

If your supply pipe is lead there should be a subsidised replacement scheme- usual deal is you dig in a new bit of placcie to the boundary and remove all lead at the house end, they remove lead and connect placcie at the main end and charge you nowt. If you get them to do the digging the price will of course go up. I've also no idea how you'd get out of the shared connection (always a bad idea).
Most combis will struggle to run 2 showers simultaneously, if this is important to you then you need to look at gravity (vented) cylinder and header tank (no point going unvented with your poor mains supply). Either have a large cylinder (250ltr) and shower pumps or (if the layout works) have a standard 150l cylinder and pump for one shower and use the combi for the other (again with 12l/min I'd advise the larger cylinder). If you plan to sort the water supply then get an unvented cylinder, plumb it with all the stuff required for unvented but use a header tank to supply it until you upgrade your water main. You can almost certainly use a boost pump of some sort between header tank and cylinder to get up to 2 bar or so but check with someone who knows ...probably not your boiler slinger who wants to sell you a combi and 2 accumulators

 

[Robotman]

If your supply pipe is lead there should be a subsidised replacement scheme- usual deal is you dig in a new bit of placcie to the boundary and remove all lead at the house end, they remove lead and connect placcie at the main end and charge you nowt. If you get them to do the digging the price will of course go up. I've also no idea how you'd get out of the shared connection (always a bad idea).
Most combis will struggle to run 2 showers simultaneously, if this is important to you then you need to look at gravity (vented) cylinder and header tank (no point going unvented with your poor mains supply). Either have a large cylinder (250ltr) and shower pumps or (if the layout works) have a standard 150l cylinder and pump for one shower and use the combi for the other (again with 12l/min I'd advise the larger cylinder). If you plan to sort the water supply then get an unvented cylinder, plumb it with all the stuff required for unvented but use a header tank to supply it until you upgrade your water main. You can almost certainly use a boost pump of some sort between header tank and cylinder to get up to 2 bar or so but check with someone who knows ...probably not your boiler slinger who wants to sell you a combi and 2 accumulators

Thanks, im going to investigate getting my mains changed. Lets see how much they charge me to get my own stop tap.

 

[Robotman]

Ok, so i've got a quote (£750) to get a 32mm blue pipe installed from pavement stop tap to my internal stop tap. Would that make any difference/improvements even if Thames water do not upgrade the lead at there end?

 

[oldbutnotdead]

Is that quote from Thames? Does it include taking you off the split supply? And have you had a look to see what is on Thames' side of the pavement stopcock-lead, steel, black or blue placcie and what size it is ish.
You will see an improvement unless Thames side of the stopcock is actually skinny lead.

 

[Robotman]

Is that quote from Thames? Does it include taking you off the split supply? And have you had a look to see what is on Thames' side of the pavement stopcock-lead, steel, black or blue placcie and what size it is ish.
You will see an improvement unless Thames side of the stopcock is actually skinny lead.

This is a quote from local moling company. It doesn't include taking me off a joint supply. Me and the neighbour will have a 32mm connection to the pavement stop tap. We couldn't see what the Thames side of the pavement stop tap has unfortunately. If we assume lead, what would that mean for me?

By the way, taking me off a joint supply is £3k min according to Thames online calculator. To get proper official price i'd have to make an application which costs £144.

 

[oldbutnotdead]

Sounds like Thames are living down to their reputation.
If the Thames side of your stopcock is 25mm or greater MDPE then even on a shared supply you'll see a significant improvement by replacing your lead pipe with MDPE.
If the Thames side is a bit of 3/4" lead then you may be rather disappointed- if pressure in the main is good (2 bar plus) then you will see an improvement but it'll be a bit better rather than a lot better. One does hear tales about water transporters keeping supply pressure down to statutory minimum to reduce losses through leaks (rather than fixing the leaks)...since there's no real competition they have no incentive to provide more than the minimum required.

 

[Robotman]

Sounds like Thames are living down to their reputation.
If the Thames side of your stopcock is 25mm or greater MDPE then even on a shared supply you'll see a significant improvement by replacing your lead pipe with MDPE.
If the Thames side is a bit of 3/4" lead then you may be rather disappointed- if pressure in the main is good (2 bar plus) then you will see an improvement but it'll be a bit better rather than a lot better. One does hear tales about water transporters keeping supply pressure down to statutory minimum to reduce losses through leaks (rather than fixing the leaks)...since there's no real competition they have no incentive to provide more than the minimum required.

Thanks for your insight on this.