Back boiler to combi

[johnad]

Hi
I will soon be moving into a property that has a back boiler fitted and I want to remove it and have a combi fitted in the kitchen
I want to do all the alterations to the pipe work myself and then get the new boiler fitted.
So my questions are after removing the hot and cold tanks etc if I link together the flow and return For the rads (pump near the cylinder)
Can I then cut into the flow and return at the kitchen rad for the connections to the boiler ?
Or is there more to it than that ?
The cold running to the loft tank obviously will feed the cold to the bathroom and the hot will then be fed from the kitchen end and just linked up in the airing cupboard for the bathroom.
I know I will need to fit thermostatic valves to the rads etc
Is there anything more I should be doing (or not)
There will be no kitchen units so access will be ok for the new boiler location and the gas is on the other side of the kitchen wall so it should be a reasonably easy job for the plumber to fit the new boiler ?
Obviously I will be asking for a power flush before the new boiler is fitted
Will the increased pressure cause any problems ?
Any advice appreciated please

 

[Dan Robinson]

A forum search would be a good place to start.

 

[bernardgreen]

If you have the tanks and they are in reasonable condition then have a heat only boiler fitted and NOT a combi.

Heat only boilers are far less trouble than a combi. Easier to service, they do not stop working if the radiator system loses pressure. the hot water tank does not limit the number of hot taps that can be open at the same time.

Some radiators will start leaking when the system is pressurised to suit the combi.

 

[Dan Robinson]

Quite a bit of twaddle there Bernard.

 

[bernardgreen]

Twaddlle based on experience.

Twaddle that several heating engineers and reputable plumbers agree with.

How many kilowatts are needed to instantly heat enough water for a decent shower ? How many more need to supply the extra water if a hot tap is turned on while the shower is in use ?

How many kilowatts are needed to keep the house warm ?

Can the combi chosen supply the instant hot water ( many kilowatts ) and also modulate down to the few kilowatts needed to keep the house warm.

If you can accept the shower water temperature changing when another hot tap is turned on or off then go with a combi. You could choose a large combi that can supply shower and a tap without a reduction in temperature of the water but it is then likely it will have to cycle on and off ( return flow too hot for efficient operation ) when just keeping the house warm.

 

[Dan Robinson]

Are you suggesting I'm disreputable?

I would also reconsider lecturing me on minimum outputs.

A combi is no more complicated than a Y plan.

They are no less reliable.

Where they do fall down is the lack of an immersion.

Everything else is a case of reading the performance charts. If the hot water performance is acceptable to the customer, then they are a valid option.

You also don't realise some combis can run the heating on open vented.


Radiators will not necessarily leak when placed under pressure.

Hence my assertion that your post was largely twaddle.

 

[bernardgreen]

I was NOT suggesting you were not reputable. I merely said that several people I know to be reputable have the opinion that a heat only boiler is the better option for almost all houses where storage tanks can be installed or are already in place.

The mention of heat outputs was not a lecture to you but information for the OP

 

[Dan Robinson]

Perhaps you should avail yourself of the performance charts of some different boilers them

 

[bernardgreen]

I did research boilers when planning the services necesary for the DIY renovation of the cottage.

 

[OwainDIYer]

Hi
Can I then cut into the flow and return at the kitchen rad for the connections to the boiler ?

Probably not; the pipes for the kitchen rad are likely to be sized for the rad only and not to carry the heat load for the whole installation.

Why don't you do the system flush yourself as that's the simplest and most time consuming part of the preparation and leave the plumbing to the plumber.

System flush requires two spanners and hosepipe, take the radiators off and into the garden and attach the hose at one end.

 

[Dan Robinson]

I did research boilers when planning the services necesary for the DIY renovation of the cottage.

Was not very thorough otherwise you'd know that most low output heat only boilers have atrocious turndown ratios due to the number of common components which control combustion.


This side of system design is more involved than you think. Google is not your best resource.

 

[bernardgreen]

The boiler I have is a Johnson and Starley.

The research included face to face chats with the J&S technical people.
Previous to that I have spoken in depth to two manufacturers of boilers in connection with the design and quality of the PCBs used in their boilers and the improvements needed.
One of my contracts was repairing PCBs for a company that supplied, installed and maintained heating systems.

 

[Razor900]

All that research and you bought a Reno??



M'lord we find the defendant guilty as charged

Ps the bloke that fitted it didn't have a big american car by any chance did he??

 

[johnad]

Thanks everyone some conflicting comments there ?
So will or will I not have possible leaks when having a combi installed in place of a back boiler ?
I'm not a big fan of having tanks in the loft hot water cylinders just take up valuable space and the existing one is very old and not very well lagged so looks like it would need replacing anyway I do like the instant hot water that I get from a combi
Along with a decent pressure at the shower ?
I have had three houses now with a combi fitted and only had a couple of small problems with them.
Looking at the system I have now the flow and return from the boiler is 22mm for about 4 feet then this reduces to 15mm this is why I way thinking that in my new property when I remove the hot water cylinder tapping into to local pipe work in the kitchen would be ok ?
Surely I don't need to extend the pipes from the airing cupboard upstairs all the way down to the kitchen to the new boiler position ?
Please keep the advice coming

 

[Dan Robinson]

It's a bit like a eunuch giving advice on the best sexual positions