combi radiator system

[monty9120]

hi all brought my first house not long ago which was fitted with a worcester bosch 28i junior combi. the old boiler used to be a back one so alot of movement took place

when i moved in some radiators were boiling some not so

i took advice from my grandad who used to be gas safe years and years ago before combis and has fit a few in his time

i learnt how to replace all the radiator valves as nearly all for the 8 rads leaked when turned

i replaced the rad in the front room with a new double one.

problem im having is the temp from the kitchen radiator is at least 15 degrees hotter then the front room. i have tried balancing but doesnt make much difference

this is a small crappy pic of the layout. the boiler runs flow and return 22mm but above the boiler it joins the existing single pipe system and reduces to 15mm all the way. the hallway radiator hardley ever works and it it does its because the radiators have turned off. trvs elsewhere

i have read that the return flow must be below 55c for the boiler to condense properly i get to this return easily.

i have to turn the boiler up to 6 or max to get any decent heat in the front room rad but means the return to the boiler is super hot

there seems to be a weird pipework to the downstairs rad too but cant be rectified

all the radiators downstairs run from upstairs. the front room and hall wall dont feed any return to the boiler. if they do its very luke warm

my grandad has said to replace the lot with 22mm simplify it a little and run 15mm to the rads. will this cure my problem?

just to let you know all the rads work just some are no where near as hot as others. the ones at the end of the line

many thanks for your suggestions

 

[monty9120]

in the pic the arrow to the left is to a rad by the boiler in the toilet

the diagram doesnt show any weird t pieces that are scattered. all pipework is 15mm

 

[stem]

problem I'm having is the temp from the kitchen radiator is at least 15 degrees hotter then the front room.

If you are referring to the return temperature, that is not unusual. It is common for a kitchen radiator to have a much smaller output than a lounge radiator, so the water looses much more more heat as it passes through a lounge radiator than a small kitchen radiator (it may be 4 times as much for example)

With balancing you may be able overcome it to some extent if you can decrease further the flow rate through the hotter radiators, so that more goes to the cooler ones.

 

[monty9120]

the temp is the heat coming off the radiator i used a probe. or the temp of the radiator itself

the lounge radiator is helped by higher temps on the boiler but balancing means i end up turning the rads off rather then getting a good temp at the rads near the end with the rest on luke warm. im sure its down to pipework myself i seem to see 22mm across is thr norm then branch off 15mm to the radiators

 

[monty9120]

just to give some feedback on this. with the amount of t pieces we decided against ripping all the pipes out as they run under the bathroom which wasnt accessible

we decided to cut the 22mm section out and fix the piping to the front room

when we stripped the floor boards up we found this

seems as though someone cocked up and fed any flow back to the return

we simplified the front room piping as i wasnt happy. cost £50 and a days work replumbed all the 22mm in the main flow and the radiator to the second bedroom

its all 15mm now. the hallway radiator that never worked very well works fine the front room radiator is red hot

ive turned the boiler down by about 3 settings and the front room still comes on

 

[simond]

Dustsheets? What did your missus say?

 

[stem]

What you show is seen frequently, and was not the result of a 'cock up' it would have been done deliberately when the system was installed to maintain the correct flow of water around the system and through the boiler.

 

[monty9120]

that would make sense but this is the second radiator near the boiler which doesnt make sense at all. the tank was removed and some piping kept which is where i feel the issue was as it looks like its all been joined together

i now have a much lower return temp on the boiler but red hot rooms wherever i desire.

the front room and hallway come on instantly now and a temp increase happens very quickly even on a lower setting on the boiler

im aware it will use more gas but i dont have cold rooms now

 

[monty9120]

having read up on the web there should be a bypass fitted. theres not and this bit of pipe didnt have one

it says if the furthest radiator is fully on which it is that will surfice.

seems bypassing via a radiator doesnt seem popular anymore

 

[stem]

there should be a bypass fitted. theres not and this bit of pipe didnt have one

Yes it did, it's the 180 degree bend shown in your photograph showing the pipe that you cut out. It joins the flow and return pipes together.

it says if the furthest radiator is fully on which it is that will surfice.

That would only be OK if the radiator doesn't have a thermostat (TRV) fitted and has lock-shield valves at both ends so that it cannot be turned off inadvertently.

Seems bypassing via a radiator doesnt seem popular anymore

Because an open pipe connection is uncontrolled and can divert flow away from the radiators unnecessarily, many systems have automatic by-pass valves fitted instead, they open only when a by-pass flow is required. They remain closed when there is sufficient flow around the radiators, like the example below.

 

[monty9120]

thank you that makes sense. as the last radiator is in my bedroom its set to 5. i renewed all the radiator valves and my bedroom does have a trv. i will take it off and fit a lockshield cap. the lockshield side is fully open

noticed today the pressure was about 3 bar in the boiler. bearing in mind its not cold and the boilers on 3 i knew there was a problem. pressed the valve on the expansion valve to a gush of water damn!!

not too bad a job on mine as the flue goes out to the left. hopefully all will be ok as the heatings been bloody ace the last week

on the expansion vessel its not in english but shows 0.5 bar thats what i set the new one too but seems low compared to what others have said online

a faulty expansion vessel is bloody heavy lol

 

[stem]

It doesn't have to be the last radiator on the circuit that is used as the by-pass. It is normally the radiator in the room where the room thermostat is located, often the hall or the lounge. That way the room thermostat controls the temperature in the room where it is located, and the TRV's look after the other rooms. With what you propose, you could end up with a very hot bedroom.

By the way. Not all boilers need a by-pass. The manual for your Worcester Bosch (or someone who knows the model) should be able to inform you. The by-pass would probably have been a requirement of the original back boiler installation.

I know what you mean about the weight of a faulty expansion vessel. At work ours was mounted horizontally and only supported by its pipe connection. When the vessel failed, it filled with water and the weight of the vessel sheared it clean off its connection and caused a major flood.

 

[monty9120]

can you advise on the expansion vessel pressure. it says 0.5 on the back.

the pressure cold is about 1-1.2 bar and doesnt seem to get above 2 bar when running now so its definitely making a difference

it says in the manual a static charge of 5 metres 0.5 bar is ok i have no idea what that means

 

[stem]

Sorry, I can't help there, but the vessels I have seen usually have a maximum pressure rating of about 10 bar and operating rating of up to 3 bar. Does the 0.5 refer to something else? if you post details of your vessel someone else may be able to help.

 

[monty9120]

the 0.5 is the pressure you need to put into the diapram in the expansion vessel when you fit it