Tried everything but luke warm radiators

[Actionmainly]

Manual valve will look like a stopcock, an automatic valve will look something like this.......

View attachment 282085

I guess you mean this? Must be manual from what you are showing

 

[Mister Banks]

I dont think that is it. The valve will connect between the flow and return pipes of the heating circuit. Its purpose is to allow flow in the case of all the radiators being turned off to prevent burning out the circulation pump.

 

[Johntheo5]

Compact 28 SE

OK then, some real info at last from the above......
The minimum output of that boiler is 19.8kw so IMO it must be cycling continuously and will never get the temperature up to its SP, in view of this suggest getting either a strap on thermometer and attach it to the boiler flow pipe or get a thermal gun to clear up once and for all what the flow temperature and boiler is doing. Ideally, monitor the return temperature as well.

 

[ericmark]

You mean turn them all off then open one at a time until lockshield side pipe heats? I have some where the lockshield side is cold the TRV side is warm and radiator is warm. It's like the heat is going in one side but not coming back out the next in order to heat the next rad? Could this be a blockage? Would a power flush possibly solve it. Really don't want to throw money at things if a new boiler would solve the problems.

If one side gets warm then there is flow, even if low. Domestic radiators are normally in parrellel not series, if the TRV's are doing there job, then the radiator may only get warm.

So back to basics, you have three controls, wall thermostat, TRV and lock shield. They need to work together, but poor settings can result in them working against each other.

 

[johnny2007]

Not a boiler engineer, but I found a similar problem at my friend's house and after much messing about with expensive calls out, it was something very simple.
All the TRV on radiators were cheap chinese things and when the head was screwed down it was pushing the pin closed or half closed.
Taking them off solved the problem.
Then they were refitted by not screwing them all the way but just up to where they engaged the pin.
Try taking the TRV head off the radiators and see what happens.
Sorry if this is not appropriate, just sharing my personal experience.

 

[Madrab]

You need to go around all the rads and open up all the lockshield valves on the rads but shut them all off at the TRV end.

Open up the furthest away rad at its TRV and fire the boiler up and see how hot it gets, if the flow from the boiler gets fully hot but the boiler shuts down before the open rad gets fully hot and the return at the boiler gets hot then there is probably a circulation issue. Try the next rad and work your way through them all and see if any get fully hot and the return to the boiler gets hot before the boiler shuts down.

If not that'll prove that water isn't getting out from the boiler fast enough or one of the boiler stats is faulty.

 

[Johntheo5]

One rad only in service will only flow ~ 6LPM even at a 6M pump head, the dT will unlikely to be less than 8C so irrespective of the rad output it will only emit ~ 3/3.5kw max or less, so the the boiler flowtemp must be less than 44C each time the boiler fires up to avoid burner cut out at 85C on fire up, might be better to start with all rad valves opened fully for a start and shut off progressively.

 

[amcluesent]

>this all started a couple of years ago when one radiator just completely stopped heating despite no messing with balancing, having the valves fully open, bleeding it and taking it off and forcing water through. <

The system maybe has problems with blockages of sediment. Was the water you poured of that radiator very dark grey/black?

A power flush may be needed.

 

[Actionmainly]

>this all started a couple of years ago when one radiator just completely stopped heating despite no messing with balancing, having the valves fully open, bleeding it and taking it off and forcing water through. <

The system maybe has problems with blockages of sediment. Was the water you poured of that radiator very dark grey/black?

A power flush may be needed.

It was I believe. I have arranged for someone to have a look at it all so hopefully it can be resolved.

 

[jeff the gasman]

Are the valves fully open?
Is there a return strainer?

 

[Actionmainly]

Are the valves fully open?
Is there a return strainer?

They are and I have no clue what a return strainer is.

 

[jeff the gasman]

Flow and return temperature at Boiler?

 

[jeff the gasman]

Weak pump or bypass stuck open having looked at schematic drawing.

 

[Ant1]

I had the same issue but on a different type of system. Just sharing in case it might point you to something useful.

I could no longer balance the system after an CH engineer changed the pipework/ system from vented to unvented, though with a system boiler rather than a combi boiler.

After spending so much money getting CH engineers / plumbers working on the issue, I decided to deal with the issue myself.

I had to take drastic actions as I really needed to sort the problem once for all:
1) All my radiators were fed from a 15mm manifold, I removed the manifold and used 22mm pipe as close to the radiators as possible (then converted to 15mm). It could be worthwhile just to only turn on a couple of radiators that you know are fed from a 22mm close by.
2) I migrated from Y to S plan as the pipework was a complete mess. With insight I think there were many airlocks. If you have compression fittings, you could slightly unscrew those to check if air comes out. You have a combi (with a single zone valve I guess) so should normally be pretty simple pipework. Maybe you could provide a photo of the pipework in this thread?

 

[Actionmainly]

So I've had a heating engineer out today. General view is its a blockage and build up of sludge in the system. Power flush isn't recommended so looking at potentially replacing the manifold installing a megnetic filter which isn't there already and putting a few litres of cleanser through a couple of times over the next few months. We may look at changing the boiler anyway but everything seems to be pointing at a build up of sludge.