W/Bosch low heat upstairs?

[laldog]

Hi all i am new here so i hope you can help.
We have a worcster bosch gas fired 28i junior wall mounted boiler.The boiler was installed 19 months ago and we have never been happy with the heat output.Upstairs rads are very poor if they are all switched on.If i switch them all off bar one the one that is left open gets red hot.This works for each and all rads in turn. have bled the system(running at 2 bar)and had w/bosch out twice.They replaced the motor twice and the second guy said the boiler was working but it was short cycling but did not know why.
The boiler is giving off 59 degrees and the return is 58 degrees.The rads closest to the boiler are red hot.I have tried"balancing" the system but this has no effect on upstairs.
The feed pipes to the rads are red hot but the return pipes are cold.The rads are new(when the system was put in 19 months ago) and the hot water side is fine.I hope i have given enough info.
By the way we did have thermostatic valves fitted to the rads but i removed these after (wrongly) thinking they were at fault.i feel as a layman the pressure or circulation is low and therefore not sending enough hot water around the system? but as i am a mechanic what do i know.



On a further note w/bosch are the most unhelpfull money oriented company i have had to deal with in a long time.

 

[Slugbabydotcom]

i feel as a layman the pressure or circulation is low and therefore not sending enough hot water around the system? but as i am a mechanic what do i know

I would consider a mechanic capable of getting to the bottom of this. You have almost answered your own question but need a bit of direction.
There's a lot of similarities between heating systems and a car engines cooling system. Heat created in the engine [boiler] is lost in the radiator and a pump circulates the water.
Focus on what you are looking for which is a blockage or cause of low flow in the circuit to the upstairs radiators.
This blockage could be caused by air, other debris or physical blockage in the system.
If it's air this can often be cleared by increasing and reducing the pressure in the system [increasing and reducing the size of the air bubble in the pipework] or venting from high points. Worcesters have an auto air vent on top of the boiler which is basically a tyre valve cap. This should be left open by about one turn.
If its debris a likely place is the flow manifold. You didn't state whether or not your system was microbore. New radiators I am told have grease in them to protect them from rotting until they are fitted. This is why systems should be flushed properly when a new boiler is fitted.
Other factors to look out for are:
That you have correctly balanced the system
Pump efficiency.
Pipe sizes
Other restrictions such as a partially blocked filter or diverter valve [notorious on Worcesters] in the boiler, isolation or zone valves in the pipework.
Might be worth investing in a powerflush!

 

[laldog]

Thanks for the reply.A couple of points you mention.How do you balance the system properly or is it just a case of trial and error.Also is this really neccasary in all cases as i would of thought the boiler to be well up to heating all the rads to piping hot.(by the way the system is 22mm down to 15mm).
Also i would have hoped the boiler/pump will be efficiant as there has been 2 new motors fitted.My plumber said it may be worth a power flush could you tell me what this entails i am guessing one pipe will be disconnected and a water feed put through to flush any debri out?
By the way the 22mm pipe only runs from the garage(boiler location) to the first floor,from there it is fed upstairs via 15mm pipe.My feeling is when all the rads are open the 15mm pipe cant return the water flow back to the boiler.The plumber said it should be fine as a lot of systems are now micro bore and this can cope.
Thanks again for any help.Laldog.

 

[Mantamad]

How many radiators/and size of radiators do you have in your house? Reason I ask is that your boiler will have a maximum capacity of water it can heat and if this is exceeded, your water will never get hot enough to heat all the radiators together but turning a few off, reduces the capacity and allows more heat. Just a thought though - it might not be this.

 

[laldog]

there are 12 rads in the system.the one in the garage is never on that is just on frost protection,the one in the kitchen is 2 foot as is the one in the bathroom.The rest are between 4 & 6 feet.
The thing is the plumbers that fitted the system said the 28i was well up to the job and they knew how many and what sizes the rads were.

 

[bab]

The boiler is well up to the job mate. There has to be a good reason for poor flow upstairs though. Normally a blockage. Diverter valves on those but i would of thought your W/bosch engineer must of checked it. to balance the downstairs rads turn all the locksheild valves on 1 end of each rad off then open only 1 rev. see if this helps up stairs.

 

[Slugbabydotcom]

Careful balancing is the way forward with this one.
bab suggests one turn. Sometimes when I balance systems I can get down to quarter of a turn on the hottest rads which are nearest the boiler.
The idea is to create an even temperature of water to all the radiators.
As the pipes to different rads have different lengths they also have different frictional resistances to the water passing through them.
A large rad has a bigger heat and therefore flow requirement than a small one.