Bloke tells me “There’s no combi Boiler in the world that’ll let you run the bath AND a shower.

Jeepers_Creepers

Snowdrops_Bluebells said:

Family of 6 here...

In our last house we had an (300l) unvented how water cylinder installed (which took about 30mins to heat up if all the hot water had been used) We only ran showers and you couldn’t tell by the temperature but the flow would drop if more than one was being used at once.

Current property has an 38kw combi and a 24kw assistant (lpg if it makes any difference) and it is the same problem- flow drops (this system is inherited, we are looking at options to alter) Our plumber seems to think we need an industrial boiler, which drained the colour from my husband’s face... Although we just tend to stagger showers to avoid the flow drop, and bang on the door really loud if the teens are taking too long! 

Replacing the shower you have with an electric one would probably be the most economic way to achieve what you want.

In your top instance, the temp presumably didn't alter because you have thermostatic shower controls. The flow, however, dropped because this unvented cylinder still needed a good mains flow and pressure to deliver the hot flow to two showers. 

In your lower case, your mains flow/pressure also isn't enough to provide for 2 combis running at the same time. Ie - almost certainly the same cause as in your previous house.

A solution to both (assuming your incoming mains supply cannot be improved by a new underground pipe) is to fit a mains booster store and pump. These have various capacities - 200L, 300L etc - and will deliver everything you could want. Yes, in theory, they too can 'run dry', but in practice they are always being replenished by the mains and have adequate capacity to cope, and will deliver the cold water to your house at awesome rates. Not silly-expensive either - around £1500? And easy to install - but ideally you'd want it in a garage or perhaps a purpose-made mini-shed, well insulated.

Or, change your system entirely... :-)

robatwork

Jeepers_Creepers said:

A solution to both (assuming your incoming mains supply cannot be improved by a new underground pipe) is to fit a mains booster store and pump. These have various capacities - 200L, 300L etc - and will deliver everything you could want. Yes, in theory, they too can 'run dry', but in practice they are always being replenished by the mains aond have adequate capacity to cope, and will deliver the cold water to your house at awesome rates. Not silly-expensive either - around £1500? And easy to install - but ideally you'd want it in a garage or perhaps a purpose-made mini-shed, well insulated.

Or, change your system entirely... :-)

Apologies for crashing into this thread but it's not unrelated. 

Let's say I have the choice of a) putting in a new polypipe to the road to replace the existing old 1940s, shared between 4 people pipe; or b) install an accumulator or mains booster. Both options would be around £2000.  Which would you recommend?

Some background info:  Flow rate 14lpm, pressure at ground level 1.5bar. Supplying a system boiler/unvented cylinder in the loft.
Plan is to increase the shower pressure from ok to great.

silvercar

We bought our house after a large extension had been completed on it. The main part of the house is served by a non-combi boiler with a hot water tank, the extension by a smaller independent combi boiler. So anyone using the shower served by the combi isn't impacted by someone using the shower served by the main boiler.
When we needed to update the main boiler, we had gas engineers look at the set up, they all agreed that it worked well and there was no reason to integrate the system into one bigger boiler.

Jeepers_Creepers

robatwork said:

Jeepers_Creepers said:

A solution to both (assuming your incoming mains supply cannot be improved by a new underground pipe) is to fit a mains booster store and pump. These have various capacities - 200L, 300L etc - and will deliver everything you could want. Yes, in theory, they too can 'run dry', but in practice they are always being replenished by the mains aond have adequate capacity to cope, and will deliver the cold water to your house at awesome rates. Not silly-expensive either - around £1500? And easy to install - but ideally you'd want it in a garage or perhaps a purpose-made mini-shed, well insulated.

Or, change your system entirely... :-)

Apologies for crashing into this thread but it's not unrelated. 

Let's say I have the choice of a) putting in a new polypipe to the road to replace the existing old 1940s, shared between 4 people pipe; or b) install an accumulator or mains booster. Both options would be around £2000.  Which would you recommend?

Some background info:  Flow rate 14lpm, pressure at ground level 1.5bar. Supplying a system boiler/unvented cylinder in the loft.
Plan is to increase the shower pressure from ok to great.

IF replacing the mains supply pipe to your house would guarantee the improvement you want, then that's what I would go for - it fixes the actual cause. Are there neighbouring houses with their own individual supply you can confirm have the F&P you are after? 

bris

You don't need to get rid of the combi, you can add an unvented cylinder to it and wire it as a Y plan.

I did this 17 years ago when I developed my upstairs. The en suit room directly above where the boiler is currently still uses it as a combi, the rest of the house is fed by the tank. At the time it was a Baxi 105 instant which packed in after 20 years excellent service. The replacement is a Baxi Duo-Tec which is a direct replacement, could event use the same jig so one off one on.

So you can upgrade to the system you need without buying a new boiler. 

Brian_Pamo

Some brilliant advice there guys.  I really appreciate your time and advice.  We have since had the surveyors report at the house we are buying and it clearly identifies the system in place at the moment.  I hope you helpful lot don't mind if I open a new thread regarding this new system and ask for answers specific to the this particular system?

the_gardener_2

If you want a beefy combi, you may need to consider if the gas main is up to the job.    
Sorry I thought I would just add to the issue.