Oil systems and plastic

[Destroyer2813]

Just trying to find out what is the reason that you cant use plastic with a oil boiler system, im a gas man myself but spoke to mate about it and he didnt know either

 

[kimbo]

You dont say where you intend to use plastic, You can use plastic on the heating as long as it is not within 1 mtr of the boiler this is written in the MI and you can use plastic pipe underground and revert to copper above ground. The problem with oil boilers is that when the boiler trips out on the high limit stat which could be 110deg the latent heat will cause the boiler temperature to rise even further and I believe plastic pipe is only good for about 120deg at 3 bar pressure, it might even be slightly less than that so you see you could have a problem.

 

[Destroyer2813]

Not me a bloke i do some subbing for wanted to use it through loft area and copper drops but the worcester book said u couldnt use plastic dont know why may well be the overheat stat as you say

 

[alexmurchison]

this is an interesting topic actually, im an oil installer but in every job i have installed, i have always used copper, or as long as existing system is ok after pressure test and clean used that. I was unawre of the restriction of using plastic. I am going to look into this, especially as someone i know wouldnt shut up with how he had just replaced his whole existing system with plastic ! I knew that you cant connect to boiler with plastic, but not sure on the rest of the system

 

[kimbo]

This is an extract from the Grant installation manual.

General - Grant boilers are compatible with both
copper and plastic pipe. Where plastic pipe is used it
must be of the oxygen barrier type and be of the
correct class (to BS 7291art 1:1990) for the
application concerned.
IMPORTANT: The first metre of pipework
connected to both the heating flow and return
connections of the boiler must be made in copper on
all types of system - sealed or open-vented..
Sealed systems - If plastic pipe is to be used, the
installer must check with the plastic pipe manufacturer
that the pipe to be used is suitable for the temperature
and pressures concerned. Pipe must be Class S to BS
7291: Part 1:1990.

 

[Destroyer2813]

Worcester manuel states do not use plastic on a sealed system but fine on open vent

 

[SimonG]

Kimbo has it spot on wrt to temps and high limit trips, but in saying that the worcester manuals do say not to use plastic on sealed systems, something that worcester can't say why! Just another get out to avoid honouring warranties.

I tend to use only copper or if using plastic I use copper until it's well away from the boiler, generally 3m away.

 

[Dannypipe]

Don't use plastic!!

What about UFH?

Plenty of oil fired Worcesters doing that.

 

[Roger Welton]

Don't use plastic!!

What about UFH?

Plenty of oil fired Worcesters doing that.

I'd imagine if you asked worcester to supply a ufh system to go on a heatslave that you would be presented with a nice load of plastic pipe.

 

[Destroyer2813]

States any underfloor heating has to go via a blending valve set at max 50c ish

 

[Dannypipe]

Yeah, but a contradicton that you can't use plastic on a sealed system with their boilers. I think it's a loads of rubbish they're spouting.

Obviously don't put any plastic directly onto the boiler and keep it a minimum of 1000mm from the boiler alltogether (or a bit more) but it's going to be fine if you stick to that.

We all know it. It's just terms and conditions to cover their backsides in exceptional cases where it may go wrong.

Only a bodger would put plastic within a meter of the boiler imho

 

[falkirkfraz]

I have been installing worcester oil fired boilers for the last couple of years and have never heard of this, it has always been plastic pipe throughout the house (unless visible) and copper pipe comes out a metre from boiler and hot water cylinder.
I have also just checked the worcester heatslave manual and found this statement:

PRIMARY SYSTEM PLASTIC PIPEWORK:
• Any plastic pipework used for the CH system must have a polymeric barrier, complying with
BS 7921 and installed to BS 5955 with 1000mm (minimum) length of copper or steel pipe connected to the boiler.
• Plastic pipework used for underfloor heating must be correctly controlled with a thermostatic blending valve limiting the temperature of the circuits to approx. 50°C with 1000mm (minimum) length of copper or steel pipe connected to the boiler, and a 20k differential must be maintained at the appliance.

 

[alexmurchison]

I have been installing worcester oil fired boilers for the last couple of years and have never heard of this, it has always been plastic pipe throughout the house (unless visible) and copper pipe comes out a metre from boiler and hot water cylinder.
I have also just checked the worcester heatslave manual and found this statement:

PRIMARY SYSTEM PLASTIC PIPEWORK:
• Any plastic pipework used for the CH system must have a polymeric barrier, complying with
BS 7921 and installed to BS 5955 with 1000mm (minimum) length of copper or steel pipe connected to the boiler.
• Plastic pipework used for underfloor heating must be correctly controlled with a thermostatic blending valve limiting the temperature of the circuits to approx. 50°C with 1000mm (minimum) length of copper or steel pipe connected to the boiler, and a 20k differential must be maintained at the appliance.

Think the problem arises from problems and rare cases where say the high limit stat has failed and boiler / pipework has exceed normal working temp. Most high liit stats trip between 95 and 110 degrees , looking at other forums some are saying not necessarily the high temp that has immediately affected the plastic pipe, but the after effects , ie pipe going brittle !! Although I presume maybe the use of a cheaper pipe had been used, probably not adequate ffor its use.

 

[keltoyboy]

Yeah, but a contradicton that you can't use plastic on a sealed system with their boilers. I think it's a loads of rubbish they're spouting.

Obviously don't put any plastic directly onto the boiler and keep it a minimum of 1000mm from the boiler alltogether (or a bit more) but it's going to be fine if you stick to that.

We all know it. It's just terms and conditions to cover their backsides in exceptional cases where it may go wrong.

Only a bodger would put plastic within a meter of the boiler imho

I have come across a few boilers (mostly landlords) where the plastic is run directly to the boiler.....not even a mm of copper in sight....and guess what no matter what u say they say whats the problem.....its working fine!!!
And one of them was in for over ten yrs.....and was a sealed system......and to be fair.... a meter away aint very far from a really hot boiler.....not a lover of plastic myself.....but its prob better than we think!!!

 

[blakeecotec]

It will work fine, but probably not installed by an competent installer as many oil boilers aren't, the idea of plastic not being connected directly to boilers is to avoid melting in certain fault conditions.i.e if they steam up. If the boiler has not been bled of all its air or the pump has an air lock it can steam up. Probably not a good idea to have plastic attached directly to the boiler at that time is a 2.5 to 3 bar the system water will reach 145 degrees before boiling, then when the expansion valve opens the pressure lowers and instant steam. The overheat won't work as well if not immersed in water. That's why it is not a great idea to have plastic near the heat exchanger of an oil fired a sealed system boiler. The amount of stored heat in 200kg of hot iron will create a hell of a lot of steam, it happened to me once years ago on a new Grant. Very embarassing, the customer was wondering why I had installed a steam engine at the side of his house.