Low mains pressure - high powered combi based system

[EliteHeat]

Hi all

Just installed a Vaillant 937 for a customer who had his rising main replaced during the works. Unfortunately there wasn't much of an improvement - his flow rate is about 12 litres/minute.

My plan now is to install two cross-fed 50 gallon tanks with a whole of house 3 bar pump rated at 20 litres per minute each side.

Painful and expensive, but IMO, no other option - any thoughts at all?

TIA
Mike

 

[Gasguru]

Whats the static pressure?

Even a new connections got to be a better solution than the propsed setup.

Otherwise if static pressures up to it maybe an accumulator.

Why wern't pressures/flowrates checked before the boiler installation - did customer but the boiler?

 

[EliteHeat]

Customer was advised that the performance of the boiler was completely dependent on the pressure/flow rate. In any event it was all in lead so had to be removed.

Customers wife also has an extremely high demand for hot water and is aware of local variations at peak times etc.

I don't think that an accumulator will solve the problem due to the demand. Customer is more concerned about constant supply as opposed to a cheap fix.

100 gallons is a fair amount, so apart from the expense I can't see the downside to this, plus 'cos he is a decent bloke I will keep it as cheap as possible.

 

[simond]

 

[Dan Robinson]

Accumulators may be the better option if the static pressure is high - what is it?

As SimonD has proclaimed in the past - no noisy pumps and potable water everywhere.

 

[EliteHeat]

Well, here I have to admit that I haven't measured the static pressure.

Mostly because I was converting the system, hanging rads, burrowing around in a crawl space where builders were busily removing (mistakenly) a load bearing wall above my head, working about 20 hours over the weekend to get the sodding thing finished to allow me to start today on a new job.

So, no static pressure but it's **** poor - just my observation!

Any comments / advice would be appreciated. I'm going to bed now.

Ta
Mike

 

[Dan Robinson]

Well what did you pressurise the system to?

 

[ChrisR]

I'd be suspicious of a blockage in the riser somewhere.

 

[Agile]

Yes, whats left between the street main and the internal pipework?

Could it be an old and resistant external stopcock?

May not be fully compliant but a full bore lever valve is a good way to make the most of a poor flow!

Tony

 

[EliteHeat]

Sorry for the delay in replying.

All internal pipework has been renewed, so 25mm MDPE immediately to 15mm Hep20 running in crawl space for approx 4 metres - no restrictions whatsoever except new 25/15 stop tap. All lead / barrel steel ripped out.

Boiler pressurised to approx 1 bar.

Don't know what the standing or working pressure is, mostly 'cos I didn't measure it. Plus with a flow rate of only about 10 litres/min it didn't occur to me. I'm not on site now, but planning to go back on Saturday.

Any thoughts on why the tanks / pump plan won't be suitable? seems like it will work well to me.

Ta
Mike

 

[Dan Robinson]

There's nothing worng with pumps and tanks - we often psec them, but they are noisy, require electric to work and do not provide potable water.

You say you have pressurised to 1 Bar so I would expect more than 10l/min from your pipe - so it sounds like there is a restriction somewhere.

Untill you do a standing/dynamic pressure test ....