I've provided a lovely new cold feed going exclusively to a new combi. A quick question.

[Mr.B]

I don't know if I have one inside the Classic. I could check the instruction manual I suppose. Obviously can't do a physical check.

I haven't said there's no F and E in the loft. There is one up there.

I've said, more than once, what my flow and pressure is. 38 litres per min and 4 bar.

I, too, have concerns about leaks but three installers say it won't and my neighbour, with a combi, has none.

 

[DP]

^^^^ Thanks for taking the trouble to come back to this.

I can obviously see what you're saying and why you're saying it. I can't and won't disagree because I don't have any arguments to offer ... but if I were were forced, on pain of death, to find some sort of logic for doing as I did I guess I'd say maybe the positioning of the 22mm branch being right at the junction of the incoming MDPE plus the increased bore almost right up to the boiler might help prevent other outlets temporarily reducing the feed to the boiler during the course of a shower.... but I may well be talking nonsense. It wouldn't be the first time.

When Tony says ..... Taking a dedicated supply directly to the combi is a very good idea for you. I can only listen to him and think presumably he has some reasoning for saying it. Perhaps he'll return and say. If I could remember who it was that made the suggestion here in the first place I'd willingly say, but it was good while back and, whilst I can just about remember what I had for breakfast, I definitely cant remember who offered the advice. But, like I say, I appreciate your thoughts.

Easiest way to answer above is as follows.

If the cold tap at furthest point is able to supply 20 l per minute and boiler and supply 13 l of hot water to that tap, does it matter where the cold connection is taken from?

At a thermostatic shower makes no difference unless mains pressure is really high in which case high mains cold pressure could affect boiler operation during shower use.

 

[Mr.B]

Understood, thank you.

 

[DP]

I don't know if I have one inside the Classic. I could check I suppose.

I haven't said there's no F and E in the loft. There is one up there.

I've said, more than once, what my flow and pressure is. 38 litres per min and 4 bar.

I, too, have concerns about leaks but three installers say it won't and my neighbour, with a combi, has none.

In that case fit a pressure reducing valve incoming mains to regulate all the feeds and ensure you have a mini expansion vessel on the cold feed into the boiler. You have more than enough cold water required for hot water delivery through the boiler.

Loss of one drop of water ( which will never be discovered) from the heating side will result in boiler needing pressure adjusted every two weeks or so.

 

[DP]

Keep the ideal classic and get an unvented cylinder. I'm constantly stunned when I go to my posh friends houses and I can't have a shower till someone else has finished or (more annoying) I have to wash my hands in cold water after I've been to the toilet.

Was about to say that.
Unvented cylinder route is what I would take plus smart TRVs on the radiators.
And a proper service to that boiler every 18 to 24 months, as described in the instruction manual ( that being the minimum task)

 

[Mr.B]

I have said above (a couple of times) that I have had a PRV on the main for the past 18 years and changed it last week for a new (drop tight) one.

I have made a note to ask the installer of any new combi if he considered a mini expansion device.

Your assertion about loss of one drop of water is most reassuring. Or not, as the case may be.

 

[Mr.B]

I don't want an unvented cylinder.

The present boiler is 28 years old and won't last indefinitely.

DP has said an unvented is prefereble - but has also said he'd be worried about pressurizing my gravity system if I fitted a combi.

What's the difference between pressurizing it with an unvented and pressurizing it with a combi? I need an answer to that.

What would your thoughts be about that?

 

[Agile]

I think you may be confusing yourself.

A boiler needs to be pressurised if the design requires it. And most modern boilers do require it.

Most radiator systems will accept a pressurised system and most installers will have pressurised many systems. I hear of few unexpected failures on pressurising.

I suppose a careful installer might drain and pressurise with air on test if they feared any system might fail.

 

[Mr.B]

I don't think I'm confusing myself. Read the parts I was referring to.

I know full well that if a boiler design requires it be pressurised then it needs to be pressurised. Did you think I can't work that one out?

I also know if a boiler (such as my Classic) is gravity fed then it runs on gravity from my Fand E.

Even I can tell a Heat Only boiler from a Combi or a System Boiler.

I even know I could pressurise my own system with an expansion vessel and filling loop and gauge etc.

I was advised, above, that so and so wouldn't fit a combi as pressuring the combi boiler might cause leaks. But I was also advised that an unvented cylinder would be better .... but that also necessitates pressuring the system as a System Boiler (with a built in expansion vessel) is the usual choice to pair with an Unvented Cylinder so how is that going to stop the same leaks occurring ?.... tell me that please, Tony.

Yes, maybe an installer might drain and do an air tight test ... I just haven't come across one to date.

And, yes, I, too, agree most installers will have converted from gravity to pressurised and the majority will have been successful. I wasn't keen to be the one exception but have said I'll take the chance.

 

[MNW67]

But I was also advised that an unvented cylinder would be better .... but that also necessitates pressuring the system as a System Boiler is the usual choice to pair with an Unvented Cylinder

It doesn't have to be. You can just as easily use a heat only boiler which is fed by the tank in the loft. All the boiler is doing is sending the water through the heating coil in the cylinder.

 

[Agile]

I don't think I'm confusing myself. Read the parts I was referring to.

I was advised, above, that so and so wouldn't fit a combi as pressuring the combi boiler might cause leaks. But I was also advised that an unvented cylinder would be better .... but that also necessitates pressuring the boiler so how is that going to stop the same leaks occurring ?.... tell me that please, Tony.

That is not necessarily true.

You could fit an unvented cylinder and quite successfully have it heated with your existing gravity fed Ideal Classic!

It is only the domestic hot water which is pressurised inside the unvented cylinder!

 

[Mr.B]

But you'll have seen me saying the boiler's 28 years old, with an inefficient cast iron heat exchanger (or so I keep being told).... and a 28 year old plastic F and E and a 28 year old plastic CWST and a 28 year old HW cylinder.and ancillaries And everyone tells me that open vent is a dirty, inefficient system which is much improved by pressurising it and doing away the the old equipment.

Believe me, Tony, I've tried to keep up but it's a struggle to sort out the wheat from the chaff.

 

[Agile]

And you can still buy heat only boilers which can be used on an open vented system.

The Worcester Ri range for example.

Altough on our energy eficiency course we were taught that an open vented system is about 4% to 5% less efficient.

 

[Mr.B]

Yes, of course you're right, Tony ... and if you went back a bit to my contributions from the past you'll see I gave (admittedly disproportionate) thought to that very thing. Intergas Heat Only was right up there as a choice. But it seems things have moved on with certain manufacturers and what WAS flavour of the month is no longer ... and you'll have seen me say, more than once that the availability of installers and spares with some makes of boiler is not the same as others. Intergas blokes are thin on the ground in this parish.

And did you not read what I just wrote about the age of the rest of the system in the house?

In your position as a long serving installer/repairer you might not notice but, even within these hallowed pages, there's a VAST amount of conflicting views and opinions (and facts) and I have been very guilty of thinking too hard and for too long. For which I'm happy to apologise for.

 

[DP]

You could fit an unvented cylinder and quite successfully have it heated with your existing gravity fed Ideal Classic!

Tony you cannot be serious.
What you are suggesting, can be done but good chance gravity circulation my not be possible with indirect coil in UV cylinder.

This scenario highlighted in a recent thread. Gravity circulation in UV cylinder almost non existent