central heating problems

[kbdiy]

Personally I would just replace the pipes like-for-like, if access is reasonable. My assumption being that it worked ok before it became blocked so why mess too much? I don't think you can use plastic due to the proximity to the boiler but the pros can give you a view on that.

Certainly that will be the cause of most of your problems and is the first thing to fix.

 

[chris5346]

is it better to increase the 15mm feed to a 22mm ?
is it worth increasing teh flow pipe from the boiler to pump to 28 mm ?
but i have 22mm pipe behind the boiler that i don't want to touch.
but i could increase to 28 at top of boiler and Tee off with 22 pipes for vent and feed then maybe a 28 into teh pump a few feet away?
to modify teh return pipes are tricky.

the boiler is only a 15kW is it worth increasing teh pipe sizes ?

i would like to try and run the pump faster so i'm thinking to raise teh water level in the expansion tank and feed pipe to 22mm maybe will prevent pump cavitating too.

i'm still unsure , before i had trv's fitted my system used to drain away in a few miniutes now it takes hours , thinking to put lockshields back on.

 

[chris5346]

suppose first thing to do is cut the T joints out and see if they are blocked and could be affecting teh flow.

the boiler pump and 3 way valve are all close to each other increasing to 28 mm wont cost much more and may stop them clogging in the future.

i would have thought 22mm feed pipe and larger expansion tank water will help teh pump ?

the pump needs a minimum inlet pressure of 1.3 M i'm thinking if i improve the water level in tank and use a 22mm feed pipe i might be able to run teh pump faster.

maybe teh 15mm pipe increases the pressure thou ? i dont want to start drawing water from the tank.

i have also noticed the 15mm pipe gets hot up thru teh airing cupboard ? is that normal heat transfer or maybe its over pumping alot and water in tank is hot also ?
i better check it out

 

[chris5346]

the 22mm vent pipe is cold where it runs up airing cupboard so it must be heat transfer causing teh 15mm pipe to get hot , but why isn't teh 22 one getting hot also when they are right next to each other ?

 

[chris5346]

maybe the 22mm vent one is hot under the floor and cools off higher up behind the emersion tank, not sure i need to investigate further .

i have also read that can put a gate valve on the feed so if i do that in 22 and find out 15 is better for the pump then i can always close teh valve down a bit.

 

[kbdiy]

The size of the feed doesn't really matter but you can increase to 22mm if you want. No point in using 28mm anywhere. It won't make any difference to the performance of the pump. The level of the water in the header tank only needs to be a couple of inches above the outlet, no more.