New Valves, inhibitor & balance yet 1 radiator needs constant bleeding..why?

[lifelearner]

We have 8 rads in total and 1 towel rail but unsure how to calculate what final pressure should be.
Over weekend bubbling sounds from top rad and variable heat.

Interestingly we've also noticed that when the hot water is turned on with the heating the tundish and overflow pipe also leak ..could this be contributing to the drop in pressure or indicative that the expansion vessel needs replacing or another problem not yet defined?

 

[Johntheo5]

What is the overflow from?.
Is the pipe in the tundish from the boiler.
Are you sure this E.vessel is associated with the boiler, Megaflow cylinders normally have a air bubble internally but will still have a Temperature&pressure relief valve venting into a tundish.

The megaflow should have another tundish??.

You can read the volume of the expansion vessel from the (should be) attached label.

 

[lifelearner]

Sorry I'm confused re your question below

The megaflow should have another tundish??

The pipe in the tundish is from the megaflow and the overflow leading outside is also from the megaflow

As I understand it this only happens if there is a fault with the pressure release valve or water pressure is too high

What I want to know is if this could be impacting what's happening with the radiators?

 

[Johntheo5]

The megaflow cylinder TPRV is normally set to 7bar, if/when the air bubble is lost then every time the the cylinder is heated/reheated this relief valve will lift and discharge a liter or so of water, sometimes another relief valve, called the expansion valve, set to 6bar is installed on the cold feed to the cylinder, this will then lift before the TPRV, I dont really know what this overflow is except that its from the TPRV, usually the vents from both the expansion valve (if installed) and the TPRV go into one tundish. any venting from these relief valves should have no effect on the primary system (rads+cylinder coil). The relief valve for this (set to 3bar) might exit through the wall behind the boiler, its a small bore pipe that may be turned back in until it almost touches the wall, this is the system that rises from 1.2 to 1.5bar or whatever.

 

[DIYWell]

Humour me. If you can access the boiler's pressure relief pipe outside, fix a bag on it with a zip tie and see if it fills up. If it just has a few drips in it after a day or so, it could be the valve needs replacing at some point. If the bag fills up, something is causing the valve to trigger and dump the pressure.

 

[DIYWell]

More humouring .... have a look at the new TRVs. Do they have arrows on them to indicate direction of flow? Most don't care, but some do. Were the lockshield valves replaced at the same time, or was it just the TRVs?

 

[lifelearner]

Hi the Lockshield valves were replaced too and the type installed are attached
Will do the zip lock bag check but I know already it's not just a drip as half the paving slab under the outlet gets wet when the pressure gets too much

 

[Johntheo5]

Have you observed the pressure rising to 3bar or near 3bar, if pressure rises to less than say 2.75bar or so and still getting a drip then the PRV should be replaced irrespective of the reason for the pressure rise.

 

[DIYWell]

Hi the Lockshield valves were replaced too and the type installed are attached

Ok, those are bidirectional valves, so we can eliminate clumsie fitting.

 

[DIYWell]

Add to your to do list, checking the pump.

When the heating has just started and the system is relatively cold, unscrew the big silver cap on the head of the pump. When the heating's running, the pump will get quite hot, so it saves you juggling a 80C chunk of metal.

You may get a bit of water dribble out, so be ready with a towel. You should be able to see the end of the shaft turning. If all is well, it will be turning at a smooth speed. If it's jerking, or oscillating, not turning, or noisy that's another thing for @Johntheo5 to ponder .