how to make the boiler work below the minimum flow...

mymedi

Hi, everyone,

I was wondering if someone might be able to comment on whether the following setup would work?

Every combi boiler has a minimum required flow rate at which it fires - if the flow is below this number (2.3-2.8 l/min or so) the boiler doesn't fire in order not to overheat.
However, this creates the issue that if the tap is only half-open, the hot water never comes - it stays cold because the boiler is not working. But if you have two taps half-open, then everything works fine.

How would I go about making the boiler work even when the flow is this low?
I was thinking of fitting a flow gauge onto the hot water supply line to read the current flow. If the flow was within a range of 0-3 l/min, the gauge would activate a brass pump that is connected to a loop branching off the hot water supply and returning back ... not sure where - maybe to the mains supply to the boiler?

What this crazy setup would do is effectively act as a second half-open tap - when the flow is low, it would boost it, thus making the boiler fire and heat the hot water...

So, would this work?
And if so, what specific parts/brands would you recommend for the flow gauge and for the pump? And where should the loop return to?

Many thanks!

Ruski

You're not allowed to pump mains pressure water, so this idea is a non starter I'm afraid.

I certainly don't have issues with having a tap on 'half' as it's above the 'minimum' flow rate, so I suggest that you measure your flow rate and then decide if you have a fault with the flow switch in the combi.

If you want a tap to trickle, then I suggest that you think about a secondary hot water supply for the individual tap in question, such as an under sink water heater.

What's the purpose of the 'trickle' tap??

HTH

Russ

mymedi

Ruski wrote: »

You're not allowed to pump mains pressure water, so this idea is a non starter I'm afraid.

Well, the loop can go into the waste drain, I suppose. The main thing is that it creates the additional flow draw on the boiler.

Ruski wrote: »

I certainly don't have issues with having a tap on 'half' as it's above the 'minimum' flow rate

To give an example, when washing up in the kitchen sink I don't want water splashing all over, so I run the tap just enough for it not to be too strong. At this rate, the flow (as measured by the flow cup, hot water only) is just under 2 l/min...
So, it's not above the minimum flow rate and the boiler does cut out.

Ruski wrote: »

think about a secondary hot water supply for the individual tap in question, such as an under sink water heater.

Since the issue is system-wide, this would have to be fitted to every tap which is very costly and a wrong kind of solution.

But thanks for the suggestions.

mart.vader

mymedi wrote: »

Well, the loop can go into the waste drain, I suppose. The main thing is that it creates the additional flow draw on the boiler.

Crazy, if you're on a meter, and prohibited if you're not.

mymedi

Why would it be prohibited if it's controlled?
Thanks.

Ruski

Well, there you go then - a perfectly good suggestion dismissed

2l/m is a ridiculously slow rate to fill a washing up bowl, my customers would be complaining if that's all they got, but hey-ho...

Maybe put an airator on the tap to avoid the 'jet' and improve the fill rate??

HTH

Russ

gmgmgm

Ruski wrote: »

Maybe put an airator on the tap to avoid the 'jet' and improve the fill rate??

This is probably what you want, OP. Your madcap scheme of sensing the flow and doubling it will probably work technically, but it's hugely over-complex.

If your problem is water splashing when you run the tap, fit an aerator to the tap. Often found on "eco" websites.

Pandilex

This is a minor pain for me, if I want to wash my hands or something, I have to turn the hot tap up quite high, and then scalding hot water comes out, so I have to turn the cold tap on too so they mix (it's a mix-tap thing), so the only way to get good temperature water to scrub my hands is if it's coming out at 900 gallons per second.

Mr_Ted

http://www.ciphe.org.uk/Global/PDF%20files/CPD2.pdf

:beer:

gmgmgm

Pandilex wrote: »

This is a minor pain for me, if I want to wash my hands or something, I have to turn the hot tap up quite high, and then scalding hot water comes out, so I have to turn the cold tap on too so they mix (it's a mix-tap thing), so the only way to get good temperature water to scrub my hands is if it's coming out at 900 gallons per second.

You could wash your hands in cold water?

lstar337

gmgmgm wrote: »

If your problem is water splashing when you run the tap, fit an aerator to the tap. Often found on "eco" websites.

My grandparents used to have these rubber snout nozzle thingies on all of there taps, I think they were something to help with splash back. Haven't seen them anywhere else, I guess they were a thing of the time!

gmgmgm wrote: »

You could wash your hands in cold water?

Exactly what I do. My OH & DD always use the hot water, but because we have a combi they wait for ages wasting my paid for water and gas.

This may be over used these days, but...