DIY Combi boiler and central heating system

[chrishob]

Hi,

I am thinking of fitting my own Combi boiler and central heating system(then a gas fitter connecting the gas). Can anybody give me a simple overall description of how to do this.

1.We are thinking of fitting the new combi boiler in the bathroom,do i simply connect a mains cold water supply to the boiler and tap in to our existing hot water pipes with the DHW connection. 2.What size plastic pipes do you run for the central heating part,do these reduce down at any point. 3.Do plastic pipes need lagging or are they thermally efficient. 4.I understand the need for a filling loop,what other stop valves or relief valves are needed. 5.Do all combi boilers have a pump internally or do some not. 6.We are not planning on fitting radiators initially,can just the DHW system be used then radiators connected afterwards. 7.Will any of our existing water pipes(hot/cold)to taps throughout our house need replacing. 8.Do combi boilers come with installation/startup instructions for the initial setup. 9.After the gas fitter has connected the boiler,should he set the boiler up and check the hot water system or is this left to yourself.

From other posts i have read about DIY central heating it seems quite

possible with some DIY experience to undertake this job,i just need to know of anything specific that should be done when fitting a system.

[Mr Fizzion]

Pretty much though because your old system probably worked at low pressure, you may need to change some of the pipe fittings and taps.

Check that the bathroom is big enough. You cannot put a boiler in Zone

1, and you may have to fit it in zone 3. Check the installation manual for this.

22mm. Tee off to the radiators with 15mm or 10 mm.

Lagging is still necessary under a suspended ground floor, in the loft or outside.

A liberal sprinkling of lever ball valves is useful for isolating parts of the system. Don't get cheap ones - they leak. Don't get gate valves - they seize.

You might need an extra expansion vessel depending on the size of your system. You need a drain point somewhere near the lowest point in the system with some sort of valve on it. An inline filter on the return from the central heating is advisable.

As far as I know they all have a pump internally.

Not very likely. You need some kind of bypass on the radiator circuit. You could probably fit just one radiator initially.

Joints that were previously under low pressure may need replacing. Compression joints may just need tightening. If the toilet was fed from a gravity system the ball valve may well fail and water will constantly drip out through the overflow.

Yes.

He will do it! He needs to check the pressure drop etc. when the boiler is running.

Yes it's quite possible...I did it with minimal experience. My best advice would be to download the installation manual for the boiler you intend to fit from the manufacturers website and read it from start to finish before you do anything.

[chrishob]

[Ed Sirett]

The FAQs below may help to address some of these questions.

[Christian McArdle]

Basically yes, provided you've removed and sealed off the old gravity gubbins.

It depends on your layout. There are various choices. You can run to manifolds and then take microbore from there to individual rads. You can run a 22mm trunk circuit and take 15mm or microbore to the rad valves. You can subzone into several zones and run 15mm for each zone. It all depends on your house layout and intended controls.

When possible, lag all pipes, whether plastic, metal, central heating, cold or DHW. This increases energy efficiency, prevents freezing and maintains hot water at the tap after a longer pause between uses.

The combi boiler will normally come with all the valves required, or describe which are missing.

The vast overwhelming majority have an internal pump. I can't think of a counterexample, but I bet someone can search out some obscure example.

Normally this is OK, although you may need to check if the boiler requires some sort of heat dumping capacity in the heating circuit.

If they do, then they were on their last legs anyway and you now have an opportunity to search for failing fittings at your own convenience.

Normally, although this can require some specialist equipment that your CORGI fitter will need to do.

Let them do it. It won't take long and it means he can sign your benchmark book and use expensive or unusual equipment for the checks (i.e. gas analysers, manometers).

Christian.

[chrishob]

Thank you for all your advice,i am sure i now have the incentive to start the job myself.Thanks again

[PM]

Before you start, find a gas fitter willing to do just the gas. Several I spoke to were only willing to do the complete job.

[chrishob]

HELP!!!!!!!!!!!!!!!

I have fitted a combi condensing boiler,i have all the connections fitted as per installation manual.i have filled the central heating(which is actually just 1 rad at the moment)with the filling loop till the guage read 1.5bar.

The combi boiler has a switch to select DHW or DHW/Central heating.

The problem is when i try to pull hot water from my taps,the burner lights and burns for approx 10-15 secs,the pressure guage rises to approx 3-4 bar and a small relief valve on the top of the boiler discharges hot steam.

There is no hot water from the taps.

I am sure everything is connected as it should be,Please help.

[Tony Bryer]

Have you forgotten to open one of the isolating valves (if it's like my Glow-worm with screwdriver valves on each pipe)

[Ed Sirett]

I don't think this is the main flow/return isolators as

1) This happens in DHW and 2) The symptoms are too extreme.

I'd go for checking that the pump is operating and that it has been bled. Clearly the auto air vent is working.

Make and model might help a bit too.

[chrishob]

Hi

How do i bleed the pump.

The model is a ravenheat csi 85a t condensing combi.

Personally i think i have air trapped somewhere in the boiler,when the burner does fire popping/air sounds come from the boiler as the pressure guage rises.

Thank You

[chrishob]

Hi

How do i bleed the pump.

The model is a ravenheat csi 85a t condensing combi.

Personally i think i have air trapped somewhere in the boiler,when the burner does fire popping/air sounds come from the boiler as the pressure guage rises.

Thank You

[John]

The pressure relieve valve is different to the auto air vent. Have you removed the dust cap from the auto air vent?

John

[chrishob]

i have found the problem,the pump was'nt running.

Just for future reference i assume pumps in new boilers are prone to sticking,all i did was tap the pump with a screwdriver and off it went circulating the central heating water.

John wrote:

[Ed Sirett]

Bleeding the pump is pretty much required and/or best practice on all combi/system boiler commissioning. The pump has a removable disc which is the bleed plug for the pump. If you had bled the pump first perhaps it might not have stuck?