Combi boiler - hot water flowing too fast, so cold.

Adrian

unread,

Feb 4, 2013, 3:55:42 PM2/4/13

to

We've just got the keys back to our house, after a couple of years in a
camper van whilst friends lived here. We've noticed something very
strange has happened with the boiler - the hot water's coming through FAR
too fast, so it's running cold. If you turn the tap way down, the flow
comes back to where it always used to be, and the temperature gets back
to hot.

It's a Worcester Bosch 24CDi Combi, just prior to condensing taking over.
A couple of years ago, a leak meant it had a new heat exchanger fitted.

Before I go ringing British Gas (it's under a maintenance contract), is
there anything obvious I can check or poke?

Ta,
A.

Tim+

unread,

Feb 4, 2013, 4:15:21 PM2/4/13

to

I suspect that the flow through the boiler was always limited by a stopcock
somewhere (maybe the main incomer) and your friends (or a plumber) has
opened it up fully after fitting the new heat exchanger.

Look for the stopcock supplying the combi and try shutting it down until
you get back to your old flow rate.

Tim

Phil L

unread,

Feb 4, 2013, 4:23:55 PM2/4/13

to

Isn't there a temp setting on the boiler for water? - they've probably
turned this right down if they had children or elderly people living there

ARW

unread,

Feb 4, 2013, 5:36:20 PM2/4/13

to

I agree. And it could be a simple as an isolation valve just before the
boiler.

--
Adam

ARW

unread,

Feb 4, 2013, 6:12:29 PM2/4/13

to

Adrian wrote:
> We've just got the keys back to our house, after a couple of years in

> a camper van.

BTW Did you have a good holiday then?

--
Adam

John Rumm

unread,

Feb 4, 2013, 6:57:18 PM2/4/13

to

Well what you describe is normal operation for many combis (unless they
include a flow regulator). In these cases one normally throttles the
water supply rate with the inlet service valve, and makes final
temperature adjustment with the taps at the point of use.

(in this weather, you won'y be able to get more than 9 lpm of usably hot
water out of a 24kW boiler).

With many boilers the temperature control for the hot water simply sets
the maximum temperature - it can't set a minimum temp.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

ARW

unread,

Feb 4, 2013, 7:05:26 PM2/4/13

to

John Rumm wrote:
> On 04/02/2013 20:55, Adrian wrote:
> > We've just got the keys back to our house, after a couple of years
> > in a camper van whilst friends lived here. We've noticed something
> > very strange has happened with the boiler - the hot water's coming
> > through FAR too fast, so it's running cold. If you turn the tap way
> > down, the flow comes back to where it always used to be, and the
> > temperature gets back to hot.
> >
> > It's a Worcester Bosch 24CDi Combi, just prior to condensing taking
> > over. A couple of years ago, a leak meant it had a new heat
> > exchanger fitted. Before I go ringing British Gas (it's under a
> > maintenance
> > contract), is there anything obvious I can check or poke?
>
> Well what you describe is normal operation for many combis (unless
> they include a flow regulator). In these cases one normally throttles
> the water supply rate with the inlet service valve, and makes final
> temperature adjustment with the taps at the point of use.

> (in this weather, you won'y be able to get more than 9 lpm of usably
> hot water out of a 24kW boiler).

It's snowing here ATM:-)

--
Adam

Ericp

unread,

Feb 4, 2013, 7:21:13 PM2/4/13

to

Isn't that boiler one that has a frame you put up and plumb then drop
the boiler into?

If so it has a full set of quarter turn taps on the frame at the
bottom front plate.

Adrian

unread,

Feb 5, 2013, 3:29:37 AM2/5/13

to

Utterly wonderful, ta. 22 countries, including Tunisia, Albania, Serbia,
Bosnia...

Adrian

unread,

Feb 5, 2013, 3:30:12 AM2/5/13

to

On Mon, 04 Feb 2013 23:57:18 +0000, John Rumm wrote:

> (in this weather, you won'y be able to get more than 9 lpm of usably hot
> water out of a 24kW boiler).

Trust me, we're getting FAR more than that with the hot tap full open.

Adrian

unread,

Feb 5, 2013, 3:30:52 AM2/5/13

to

On Mon, 04 Feb 2013 21:15:21 +0000, Tim+ wrote:

> I suspect that the flow through the boiler was always limited by a
> stopcock somewhere (maybe the main incomer) and your friends (or a
> plumber) has opened it up fully after fitting the new heat exchanger.
>
> Look for the stopcock supplying the combi and try shutting it down until
> you get back to your old flow rate.

I like that idea. It's nice and simple.

I shall rummage.

Adrian

unread,

Feb 5, 2013, 3:31:35 AM2/5/13

to

On Mon, 04 Feb 2013 21:23:55 +0000, Phil L wrote:

> Isn't there a temp setting on the boiler for water? - they've probably
> turned this right down if they had children or elderly people living
> there

Yes, there is - and it's turned up. When you turn the tap flow down, the
water is proper hot.

Dave Liquorice

unread,

Feb 5, 2013, 4:42:32 AM2/5/13

to

On Tue, 5 Feb 2013 08:30:12 +0000 (UTC), Adrian wrote:

>> (in this weather, you won'y be able to get more than 9 lpm of usably
>> hot water out of a 24kW boiler).
>
> Trust me, we're getting FAR more than that with the hot tap full open.

Make your mind up:

" ... the hot water's coming through FAR too fast, so it's running cold.

If you turn the tap way down, the flow comes back to where it always
> used to be, and the temperature gets back to hot."

So is this high flow of water "useably hot" or not?

--
Cheers
Dave.

John Rumm

unread,

Feb 5, 2013, 5:29:48 AM2/5/13

to

Well to quote Scotty, "yea cannea change the laws of physics!", so if
its coming out much faster, than that, its not going to be hot. Which
brings us back to your original problem.

David.WE.Roberts

unread,

Feb 5, 2013, 6:25:00 AM2/5/13

to

Been watching this for a while.

Isn't a tap an analogue rather than a digital device?

So what is the problem with turning the tap on just enough to get the
water temperature that you want?

Cheers

Dave R

dochol...@gmail.com

unread,

Feb 5, 2013, 10:36:06 AM2/5/13

to

On Tuesday, February 5, 2013 11:25:00 AM UTC, David.WE.Roberts wrote:
<snip>

> Isn't a tap an analogue rather than a digital device?
>
> So what is the problem with turning the tap on just enough to get the
> water temperature that you want?
>

If there's any length of pipe between the boiler and the tap the lag between changing the flow and observing the new temperature makes it quite a long process to get the temperature you want - if there's a flow restrictor upstream that you can set just the once it makes things easier.