Unvented water off a combi boiler?

[Onetap]

It is plain you can't understand something so simple.

The only thing you need to understand here is that BigBurner is Dr Drivel operating under another name, he is posting his usual ill-considered drivel, he is simple and he cannot grasp the many failings inherent in his half-wit schemes.

For example

Feeding pre-warmed or hot water back into the cold water feed connection on a combi assumes that the cold inlet components on the combi are rated for hot water; many of them aren't.

Fit a bronze pump on the pipe from the bottom of the cylinder pumping into the combi.

The conection for the bronze pump would have to be from the bottom of the cylinder. The only connection there is usually the cold feed.You'd be pumping from the cold feed back into the cold feed; impossible. You will also have entrained limescale particles in hard-water areas; this will knacker your combi plate heat exchanger and your canned rotor bronze pump in a short time.

It also assumes that a bronze canned rotor pump will produce enough head to produce the minimum flow rate through the high hydraulic resistance of the combi plate heat exchanger.

The major problem is that most combis use a diaphragm-actuated diverter valve to fire the combi on a hot water demand. This only works when a tap is turned on. Putting in a re-circulation system, as Drivel recommends, will not operate the diverter valve and will not make the combi fire up.

The man's a fool; ignore everything he recommends.

As mentioned above, put in an indirect unvented system with an S-plan plus control/wiring system. This works, I've done it.

 

[clf-gas]

AWE!!!!

Your spoiling me fun Onetap

 

[Paul Barker]

when drawing hot water some flow would go through combi unless you use A and a zone valve between A and combi opened by cylinder stat zone valve powers pump and instructs combi there is flow? Ideally get a ylinder with a secondary return put the output of combi in there to discourage hot water draw from sucking straight from combi when the temp of cylinder brops to trigger point during hot water draw.

It is a nice idea but it needs practical testing.

For the extra cost of an indirect cylinder a much less troublesome method would heat the cylinder / rads using y or s plan, take dhw from cylinder feed cylinder from combi.

 

[BigBurner]

when drawing hot water some flow would go through combi unless you use A and a zone valve

A simple check valve after the pump will do.

It is a nice idea but it needs practical testing.

It has been tested. I used one. As Onetap man mentioned the combi needs to be suitable for a hot water cold feed. Many are these days. All Alphas are to my knowledge.

For the extra cost of an indirect cylinder a much less troublesome method would heat the cylinder / rads using y or s plan, take dhw from cylinder feed cylinder from combi.

Troublesome? Connecting a combi directly and fitting a bronze pump is simplicity itself. No zone valves, complex control wiring etc. Look at the performance of super fast recovery and not running out of DHW. The cylinder can be downsized too. It is also cheaper. It is a win, win all around. Mr Barker you are one of the more intelligent posters - pay attention at the back

 

[BigBurner]

So does the cold mains feed connect at point A or point B.

View media item 6531

It connects directly in the normal way.

 

[ChrisR]

There are several differences between the Plateflow, which works, and Drivel's mess, which doesn't.
Things could be added to what he says to make it work, but I can't be bothered to spend the time thinking about it.

The combi will deliver 60C of heat

It has been tested. I used one.

He probably means it heated water up. Anyone who posts as he does, obviously isn't capable of analysing his own output, whether it's words or hot water.

 

[BigBurner]

It is plain you can't understand something so simple.

The only thing you need to understand here is that BigBurner is Dr Drivel operating under another name,

He is? New to me. Now let's see what this one is on about....

Feeding pre-warmed or hot water back into the cold water feed connection on a combi assumes that the cold inlet components on the combi are rated for hot water; many of them aren't.

Get one that can - most can these days.

Fit a bronze pump on the pipe from the bottom of the cylinder pumping into the combi.

The conection for the bronze pump would have to be from the bottom of the cylinder. The only connection there is usually the cold feed.You'd be pumping from the cold feed back into the cold feed; impossible.

Most have two ports. Use a Surrey flange in only one.

You will also have entrained limescale particles in hard-water areas; this will knacker your combi plate heat exchanger and your canned rotor bronze pump in a short time.

All Combi plate heat exchangers work with fresh water. Did you know that?

It also assumes that a bronze canned rotor pump will produce enough head to produce the minimum flow rate through the high hydraulic resistance of the combi plate heat exchanger.

It does. Fit as close to combi if you think there will be problems. Most modern combis just require a slow flow anyhow.

The major problem is that most combis use a diaphragm-actuated diverter valve to fire the combi on a hot water demand.

Few work on this principle these days. It is not 1985 anymore. This displays a distinct lack of knowledge.

Poor show. Your knowledge and reasoning is poor. The bit about a bronze pump, pumping back into a cold main proves your reasoning is just about absent. Try harder next time. Think before you type, or ask questions.

 

[BigBurner]

There are several differences between the Plateflow,

There is not. The only constraint is that the combi will deliver 60C maximum in DHW temp. A plate heat exchanger is well, er, er, er, a plate heat exchanger, whether inside the case or outside. Got it?

 

[clf-gas]

So does the cold mains feed connect at point A or point B.

View media item 6531

It connects directly in the normal way.

So connect cold feed to combi ("normal way"). How is the cylinder being replenished, hang on!!!!!! it wont need to as the combi is acting like a errrrr, combi.

Connect cold feed to cylinder, hot tap opened and cold replenishes cyl, argh got you. How you stopping the combi kicking in in this case.

 

[ChrisR]

ChrisR wrote:
There are several differences between the Plateflow and Drivel's mess,

There is not.

There are, it's just that you're too dumb to notice or realise the importance.

All Combi plate heat exchangers work with fresh water. Did you know that?

BUt they don't recirculate limescale particles through their own plate heat exchanger.
The hex is designed to make then unstick and get washed away out of a tap.

The only constraint is that the combi will deliver 60C maximum in DHW temp.

Oh dear. WHat flow rate will a 24kW combi do that at, in the winter?

One reason the Plateflow doesn't mix COLD water (much) from the cylinder withthe output from the cylinder is the control of the bronze pump's flow rate, which you don't seem to have realised anything about. 1)The water from the Plateflow's plate heat exchanger need to be HOT, so that a certain amount of cold water from the cylinder can be mixed with it and still be hot enough for DHW purposes.
Only stratification in the cylinder stops cold water from the cylinder, mixing with the hot.
The geometry of the connection is also relevant.

Get one that can - most can these days.

NO, most can't.

The conection for the bronze pump would have to be from the bottom of the cylinder. The only connection there is usually the cold feed.You'd be pumping from the cold feed back into the cold feed; impossible.

Not a problem in fact - it wouldn't matter where the T were.

Most have two ports. Use a Surrey flange in only one.

On the cylinder input - oh well thought through. a) cylinders do NOT have two entry ports, b) it isn't necessary c) is this something you just only just thought up, "apart from a £50 pump"?? I note you're suggesting an unnecessary check valve as well.

DHW flow reverts to what the combi can provide at a lower flow rate. Two stage flow rate.

There's nothing controlling the flow rate, so you get frozen while you play with the taps and jump out of the shower while the pipe empties

Got it?

We've got it, Drivel. Whatever it is that you have that we haven't, nobody wants.

 

[BigBurner]

So does the cold mains feed connect at point A or point B.

View media item 6531

It connects directly in the normal way.

So connect cold feed to combi ("normal way").

No. Cold feed to cylinder only. Combi only reheats cylinder water.

Connect cold feed to cylinder, hot tap opened and cold replenishes cyl, argh got you. How you stopping the combi kicking in in this case.

The cyl' stat keep the bronze pump off until the temp in the cylinder drops. Combi only operates when pump is on.

 

[BigBurner]

This ChrisR fella.

Again..There is no difference to Plateflow.

The combi only reheats the cylinder and will acts as a combi when cylinder has no hot water. What can't you understand about that?

A restrictor can be fitted in-line as per usual to get the flow through the combi Common sense.

Tried and tested and anyone with half an engineering brain can figure it out. The precludes you. Some makers recommend it.

There's nothing controlling the flow rate,

Like most combis.

How is the bathroom changing going?

 

[clf-gas]

View media item 6537

So if mains cold feed is connected at cylinder, then where is the feed to pump and combi coming from.

 

[Onetap]

You will also have entrained limescale particles in hard-water areas; this will knacker your combi plate heat exchanger and your canned rotor bronze pump in a short time.

All Combi plate heat exchangers work with fresh water. Did you know that?

You do not understand, Drivel.

The limescale is dissolved in the cold fresh water. The limescale particles precipitate inside the cylinder when the water is heated and accumulate at the bottom of the cylinder. Pumping from a connection at the bottom of the cylinder will pump the particles into the combi and the bronze pump.

 

[Onetap]

It also assumes that a bronze canned rotor pump will produce enough head to produce the minimum flow rate through the high hydraulic resistance of the combi plate heat exchanger.

It does. Fit as close to combi if you think there will be problems. Most modern combis just require a slow flow anyhow.

Oh dear, we seem to be suffering a a complete incomprehension of pump sizing. I'm not even going to try to explain why fitting it 'closer to the combi' will not make one iota of difference.