Re-plumbing the central heating.

[pippo]

Hi folks,

A few months ago we had a worcester bosch 28i junior boiler fitted which was replacing a back boiler system. The heating side was fitted to the old microbore pipework. I have noticed that the pipes to each rad which get hot first (I presume these are feed pipes) do not go to the trv side on all rads. The microbore is looking old and corroded in areas and I have fixed 4 leaks since the new system was put in. The pipes are also way longer than they need to be and dangle on the ground downstairs with no insulation under a ventilated suspended floor. Due to this and the fact that the pipes running upstairs are in a ventilated/cold chimney with no access to insulate them, I wish to replace/re-route all the pipework before we put down new carpets etc. Before I do this I thought I would ask some questions.

1) Would it be best to remain with 22mm feeds then microbore? the house is a small 2 bed semi with 6 rads. 4 downstairs and 2 upstairs (downstairs bathroom) or would a larger bore be better? perhaps plastic?

2) Should all feed pipes to each rad be on the trv side?

3) Does the system need a PRV on it to stop pressure build up? There was none fitted by the company who fitted the boiler. I plan on fitting a towel rail, if i do not have a trv on the towel rail, will this allow the water to constantly flow and thus no need for a PRV? or will this lead to the boiler being constantly on and inefficient?

4) Can I "T" piece the feed and return pipes near the boiler and send a feed and return upstairs to 2 port manifolds to do the 2 rads and also a feed and return going to 4 port manifolds for the downstairs 4 rads? At the moment the feed and return go to manifolds downstairs then continue out the manifolds and upstairs to the next manifolds.

Any answers you can give me would be excellent. I am sorry if this is unclear as I am pants at writing stuff. If you need more info please ask.

Many thanks in advance

Pippo

 

[sambotc]

1) Would it be best to remain with 22mm feeds then microbore? the house is a small 2 bed semi with 6 rads. 4 downstairs and 2 upstairs (downstairs bathroom) or would a larger bore be better? perhaps plastic?

Personally i would rip out all the microbore and replace with 22mm/15mm as required.

2) Should all feed pipes to each rad be on the trv side?

Not necessarily. If the trv's are bi-directional they can be fitted on either the flow or return. If you look at the TRV valve body itself, there should be an arrow indicating flow direction. If there are 2 pointing in opposite directions then they are bi-directional. Usually if they are fitted the wrong way round they will be noticably noisy.

3) Does the system need a PRV on it to stop pressure build up? There was none fitted by the company who fitted the boiler. I plan on fitting a towel rail, if i do not have a trv on the towel rail, will this allow the water to constantly flow and thus no need for a PRV? or will this lead to the boiler being constantly on and inefficient?

The PRV is fitted within the boiler itself. There is a connection on the bottom of the boiler which should have a 15mm copper pipe coming off it and through the wall outside, which should then be turned back to the wall. Has this been fitted? If not get the installers back to rectify!
fitting a TRV on the bathroom rad has no effect on what the PRV does or act's.
At least one radiator should have NO trv to act as a by pass. Also a room stat should be fitted to comply with part L building reg's. The area in which this is fitted should have no TRV.

4) Can I "T" piece the feed and return pipes near the boiler and send a feed and return upstairs to 2 port manifolds to do the 2 rads and also a feed and return going to 4 port manifolds for the downstairs 4 rads? At the moment the feed and return go to manifolds downstairs then continue out the manifolds and upstairs to the next manifolds.

As above consider running all radiators off 15mm and 22mm. General rule of thumb is 14,00btu's to 15mm max.

Hope that helps, Sam

 

[pippo]

Sam,

Many thanks for your reply. Very helpful indeed.

There is a copper pipe going through the exterior wall from the boiler as you described. The trvs do have only 1 arrow on them that I can see so I will place them on the feed side to be sure. There is no thermostat at the moment however I was informed at the time that my boiler is compatible with a wireless thermostat. Based on all this info here is my plan:

1) Run main feed and return pipes in 22mm and "t" them off, with a 22mm feed and return for downstairs and a 22mm feed and return for upstairs.

2) Place the downstairs and upstairs manifolds as centrally as possible so that the distance to each radiator is equal.

3) Run 15mm pipes to the radiators with as short runs as possible and place the trvs on the feed pipe side (as unsure id bi-directional trvs).

4) Have no trv on the hallway radiator to act as a bypass and place the wireless thermostat in the hallway. (this radiator heats the small hallway, the stairs and the very small landing at the top).

5) Insulate all pipes under the vented suspended wooden floor downstairs.

Does this sound about right? Would using plastic throughout be sufficient for this setup?

Thanks again

Pippo

 

[sambotc]

Sam,

Many thanks for your reply. Very helpful indeed.

There is a copper pipe going through the exterior wall from the boiler as you described. The trvs do have only 1 arrow on them that I can see so I will place them on the feed side to be sure. There is no thermostat at the moment however I was informed at the time that my boiler is compatible with a wireless thermostat. Based on all this info here is my plan:

1) Run main feed and return pipes in 22mm and "t" them off, with a 22mm feed and return for downstairs and a 22mm feed and return for
upstairs.
Sounds sensible!

2) Place the downstairs and upstairs manifolds as centrally as possible so that the distance to each radiator is equal.

You don't use manifolds with 22/15 just use reducing tee's off the 22mm. Although keeping them central and keepin distance equal is good practice, it's not essential. This will help the system balance itself better but may be more work/expense in doing so.
It's normally easier to route pipework using the simplest/easiest/most cost effective way and balance the radiators as required once complete and running. This is simply achieved by closing off the lockshield valve on some radiators to promote flow towards radiators which may have pipe runs with more resistance. If that makes sense!?

3) Run 15mm pipes to the radiators with as short runs as possible and place the trvs on the feed pipe side (as unsure id bi-directional trvs).

Yep

4) Have no trv on the hallway radiator to act as a bypass and place the wireless thermostat in the hallway. (this radiator heats the small hallway, the stairs and the very small landing at the top).

Should really have been completed by the boiler installer, as it is a requirement

5) Insulate all pipes under the vented suspended wooden floor downstairs.

Will save a few pennies!

Does this sound about right? Would using plastic throughout be sufficient for this setup?

Plastic is personal preference. For a novice it would be easier and less likely to encounter problems installing providing you follow the instructions! Personally i would always choose copper but more likely to encounter problems if you can't or have never soldered before. Both have there own benefits and disadvantages.

Thanks again

Pippo

HTH Sam

 

[AMEdinburgh]

From a DIYer not plumber.

I believe you MUST have the pipe connections to the boiler in copper for a set distance (1m?) You can then connect to your plastic with an ordinary brass compression fitting.

I am sure sambotc will tell you whether I'm on the right track or talking cobblers.

I've done two full heating plumbs, one in end fed copper & one in Hep2o plastic and both are 12 years old and no leaks on either, so far, touch wood.

 

[AMEdinburgh]

Another thought that you might or might not have already taken into account.

Changing copper to plastic may mean you need to provide earth bonding for each of your radiators as you will have lost connection to earth through the pipes.

If you're not sure you might add a post to the electrical section

 

[pippo]

Thanks AM,

I had read somewhere that some of the pipe from the boiler had to be copper, it is at the moment and i will leave that section in. Its 22mm anyway. With regards to the earth bonding, I will have to run an earth to all the radiators. There is no earth bonding at each radiator at the moment and the existing system is part plastic on the main feeds so no continuous earth grrr. Seems that the crowd who were in here didnt do a great job. May get a pro in to check the boiler and gas as I no longer have confidence in the job.

In terms of the earth bonding, can i run it in series from rad to rad in standard earth cable and leave the end near the consumer unit and have a spark fit it?

 

[D_Hailsham]

In terms of the earth bonding, can i run it in series from rad to rad in standard earth cable and leave the end near the consumer unit and have a spark fit it?

Supplementary bonding is only required in a bathroom, kitchen etc. It is not necessary in living rooms bedrooms etc.

Read Earth Bonding for more information.