Converting from regular to system boiler

lohr500

We replaced our 35 year old + oil boiler last year.

A lot of our pipework is buried under concrete and until we moved into the property, the spring water supply had no pH correction and was quite acidic. After experiencing a number of pinhole leaks in the pipework (fortunately all in accessible places) and green coloured baths (copper leaching out of the hot water system due to the acidity of the water), I installed some pH correction.

Given the fragile nature of our pipework, I decided to stick with a regular boiler!! The thought of high pressure in our system worried me greatly. So much so, that I asked the installer of the new boiler not to do any power flushing of the system. Instead we did several gravity flushes of the radiator system over a period of three of four weeks, adding flushing chemicals to assist the process.

We have a low pressure pumped supply from the spring water holding tanks to two header tanks in the loft. Then gravity takes over. Both the tanks in the loft are made from some sort of plastic and remain sound after probably 35+ years.

Tempting fate, but I'm far less worried about a leak from the loft than pipework leaks in the concrete under our kitchen floor or behind walls. 

With our cylinder, it already had a thin lagging jacket when we moved in. I just bought an oversized jacket and put this over the existing one. The cylinder is in a small airing cupboard so a little bit of heat loss isn't the end of the world. It keeps the towels, blankets and spare pillows aired. If your cylinder is in good order, it will probably cost a lot less to chuck a load more insulation around it, than to replace with a modern expanded foam encapsulated one

I also like regular boilers as there is less to go wrong!! Just by replacing our ancient oil boiler with a modern efficient unit and changing the heating/hot water system to "S" plan, we are saving 30% in our oil consumption. 

markin

Old pipes and rads are not likely to like a power flush needed for the boiler swap or being under pressure, has it got steel pipes or is it all copper?

Ultrasonic

Nymbus said:

What do you mean by “OP”?

OP just means Original Poster i.e. you. (Also sometimes Original Post.)

Sea_Shell

We had our "old skool" 1991 gas boiler replaced with a "system" boiler in the summer.

No issues as far as I know, it's working fine.    No one mentioned "high pressure" to us, but I know its a sealed system, and we have a little pressure gauge to monitor with isolator valves, so we can add water if we notice the pressure dropping.  

It usually hovers between 15-18 psi depending on the temperature in the system.     This doesn't sound like "high pressure" to me.

I think my SiL has a fully pressurised system, and I think this is something different.

For us, It was a really simple change over, and we've not noticed any change in the way the system works, other than it being more efficient and much quieter.

MWT

Sea_Shell said:

It usually hovers between 15-18 psi depending on the temperature in the system.     This doesn't sound like "high pressure" to me.

That is about 2-3x the pressure in an open vent system, so significantly higher, and it is that increase that is a concern with older pipework and radiators.

As long as you are not frequently seeing the pressure drop then you are OK.

Sea_Shell

MWT said:

Sea_Shell said:

It usually hovers between 15-18 psi depending on the temperature in the system.     This doesn't sound like "high pressure" to me.

That is about 2-3x the pressure in an open vent system, so significantly higher, and it is that increase that is a concern with older pipework and radiators.

As long as you are not frequently seeing the pressure drop then you are OK.

OK, thanks.

Fingers crossed then!!!! 

Astria

Nymbus said:

So replace with a new regular boiler and cylinder then? 

That would be the easiest and least likely to cause problems way of going.

doodling

Hi,

MWT said:

doodling said:

If a CH system cannot stand being converted to a sealed system then it needs fixing anyway. 

Why? .. a low pressure system, often buried under concrete that is giving no cause for concern does not need replacing.

You don't know if you have a problem until you pressurise the old pipes and rads, by which time you may have a problem which wasn't an issue before...

The reason I say that is that the plumbing (not the radiators though!) in good condition should be good for at least 5, probably 10bar (annealed 28mm copper pipe is good for 27bar, lower diameters can handle higher pressures). Plastic is generally rated for 3 bat at 100C.

If it can't withstand the 1 - 1.5bar of a sealed system (i.e. between a quarter and a tenth of what it should be capable of)  then the pipework is seriously degraded and is likely to fail soon in any event.

The argument then is whether the OP wants to have all the disruption at the same time or whether he wants to replace the boiler now and then any dodgy radiators / pipework later. This choice will be determined by their budget and general views which I hesitate to predict.

Personally I would want the confidence that I had a heating system that didn't have any known weak spots so I wouldn't mind if they were found and fixed when converting to a sealed system but I accept that others may have different views.

MWT

doodling said:

Personally I would want the confidence that I had a heating system that didn't have any known weak spots so I wouldn't mind if they were found and fixed when converting to a sealed system but I accept that others may have different views.

It all comes down to motivation and your risk appetite / budget.

Your pipework doesn't have to be 'seriously degraded' to leak under the increased pressure, it just needs one bad joint or a pin-hole weakness in a pipe and you will have a problem.

... but if there is no particular need for a sealed system then there is little to gain from the unnecessary risk, but if you are already in the process of major redecorating, taking up floors etc. then it may be justified in an older property.

matelodave

most pressurised systems run at around 1- 1.5 bar = around 15-22 psi which is roughly equivalent to having the tank in loft at around 15 metres above the ground (thats around 49 feet)

I'd guess that most tanks in the loft are only around 5-6 metres above the ground giving a pressure of about 0.5bar = 7psi, so you are likely to be doubling or even tripling the pressure of your existing system.

In most cases it wont cause a problem but it can be if the system cant take the extra pressure and finds a poor joint or pin hole.