Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Help-whats the best thing to do? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1107193861 Message started by peter on Jan 31^st, 2005, 5:51pm

Title: Help-whats the best thing to do?
Post by peter on Jan 31^st, 2005, 5:51pm

Ive got a vaillant 637 boiler and vantage 150ltr water cylinder fitted. This is an unvented system.

The plumber has also fitted a bronze pump for circulating the domestic hot water around the house. Its a two bathroomed
house which has two thermostatic showers.

The plumber has advised that this pump can be wired in order to stay switched on all the time thus enabling hot water from the tap at demand.

However ive also been advised by a friend that this will cool the water in the storage tank making the system work uneconomically, as the boiler will have to reheat the water which has been cooling having left the cyclinder.

Can any wise person tell me the best way to wire this pump ?

Many Thanks. ??? ???

Title: Re: Help-whats the best thing to do?
Post by greg on Jan 31^st, 2005, 7:14pm

The pump should be wired so that it only circulates when needed - usually done by means of a time clock and a pipe stat

Title: Re: Help-whats the best thing to do?
Post by JerryD on Feb 1^st, 2005, 7:46am

wrote on Jan 31^st, 2005, 7:14pm:

The pump should be wired so that it only circulates when needed - usually done by means of a time clock and a pipe stat

But doesn't this mean that you've still got to wait for hot water at taps with a long leg of pipework to them? I always thought 'circulating' hot water was always pumped continuously (perhaps off at night or other times when house is unoccupied).

I assume you recommend 'timed pump' in this situation as this is a domestic dwelling rather than a hotel or similar?

If the pipe runs are heavily lagged then the heat loss would be minimal (no worse than the water in the actual cylinder). The beauty of this system is that you get 'instant' hot water from a hot tap which is miles away from the hot cylinder.

I have considered this system for my own house as we have a bathroom with a long run back to the cylinder. If the pump is controlled by a 'stat', how quickly would hot water appear at a distant tap?

Title: Re: Help-whats the best thing to do?
Post by greg on Feb 1^st, 2005, 6:19pm

Jerry,

Pump would run continuously according to time clock and stat settings - purpose of these is to ensure that it is only running when necessary if the water is returning to the cylinder at 65 degrees then the entire "loop" is at 65 degrees so the pump can switch off, gravity circulation will then take over, return temp drops below stat setting, pump starts up again, temp rises in the loop, pump switches off etc etc - night time comes and time clock switches off the pump / stat set up

This set up will mean the only cold water you have is that in the draw off pipe from the loop which you would keep to a minium, certainly no more than a couple of meters

Hope that makes sense

Title: Re: Help-whats the best thing to do?
Post by JerryD on Feb 1^st, 2005, 7:01pm

Hi Greg, I get it now! Sounds good.

Will 'gravity circulation' take over when the pump is off? In other words, doesn't the pump itself act as a barrier to the gravity circulation?

What current does a little bronze pump draw? It can't cost much to keep it running continuously (just using a timer for main off periods) ? This would then save the need for a stat?

Are my ideas rubbish ;D Just trying to get me head around what I can do here at JerryD towers ::)

Title: Re: Help-whats the best thing to do?
Post by PEDANTICVINDICTIVEMAN on Feb 1^st, 2005, 7:07pm

Gregs idea sounds the thing to me, cant see why you would need instant hot water in the middle of the night unless you shiitte the bed :)

Title: Re: Help-whats the best thing to do?
Post by greg on Feb 1^st, 2005, 9:27pm

Jerry,

Go to www.grundfos.co.uk and do a search for "comfort" then select product range from the search results - these are all bronse pumps, ideal for secondary returns, you'll notice that you can buy them as a basic pump or pump & timeclock or pump, timeclock stat

Hey PVC man - long time no see here

Title: Re: Help-whats the best thing to do?
Post by JerryD on Feb 1^st, 2005, 11:32pm

wrote on Feb 1^st, 2005, 9:27pm:

Thanks greg, this looks like what I need. Shall have to do a costing now :(

Title: Re: Help-whats the best thing to do?
Post by PEDANTICVINDICTIVEMAN on Feb 2^nd, 2005, 7:39am

Not been anything really interesting on here recently, spending a fair bit of time on DIYnot.com

Title: Re: Help-whats the best thing to do?
Post by thescruff on Feb 5^th, 2005, 1:34am

wrote on Feb 1^st, 2005, 7:01pm:

No;because there should be non-return valve fitted between the cylinder and pump to avoid reverse drawoff

Title: Re: Help-whats the best thing to do?
Post by CWatters on Feb 8^th, 2005, 7:14pm

I believe what you have is called a "secondary loop".

Usually found in hotels where the distance from hot water tank to tap is long.

It's not ususally intended to increase the water pressure just reduce the time it takes for the hot water to get to the tap. It's a nice feature to have.

Without the pump or with it off you have to wait longer for hot to come out and that wastes metered water.