Plumbing oddness

The Flexible hose has an isolator at the right-hand end which is used to top up the water in the system, it’s closed most of the time – I’m assuming this has started to let water past which is causing the pressure to build in the system. I’m happy to replace this myself (using the massive isolator first), but I’ve never seen one that looks like this before, anyone know what it is and where to get one?

Looks like a standard combi filling loop (available pretty much everywhere - Screwfix, Toolstation, probably even B&Q).

You can verify / rule out the filling valve as the cause by removing one end of the flexible hose (makes sure that the filling valve is off, and also the one at the other end of the flexi pipe if there is one, then unscrew either of the fittings with 'ears'). If it keeps dripping from the pipe on the right, then that may be the problem. On the other hand, if the pressure continues to rise with the flexible pipe disconnected, it might be that the heat exchanger in your boiler has failed.

For the leaky TF1, try quickly opening the valve then shutting it again (before you disconnect the filling loop so that you can top the pressure up again if you lose too much water).

IANAP

Disconnect the flexible hose and fit a 1/2” blanking cap on each end where the hose goes. Simplest solution and requires no draining of anything.

Thank you both for the comments.

I'll have a play later, although Tillydog has reminded me that we had a similar pressure issue a 2-3 years ago and a new expansion vessel was fitted.  Hope that hasn't gone again already.

I had a very quick open-close-open-close session with the TF1 and it seemed a little better (still dripping but def not as often).  I then had another go and it's back to where it was initially 🙁  I didn't have much time, so will try that again later, hopefully there's just a bit of crud in there that'll shift eventually.

I had the exact same issue with a dripping valve on the filling loop and rising pressure.

In the end it was two separate issues...

I got the hose and valve replaced and it fixed that issue. Apparently they just randomly go sometimes 🤷‍♂️

After that though, I still had pressure rising in the system.

That turned out to be the internal bladder in the expansion vessel the boiler. The pressure in these sometimes needs resetting, which you can do yourself with a track pump (which we all have there right? 😁)

Plumbers will want to replace the vessel, but it's often just pressure reset that's needed.

I watched a few YouTube videos and it was very easy. Been fine for over a year now.

The flexible hose should be disconnected, at one end, at least, when not in use. The original guidance stems from the risk of introducing legionella from your heating loop back into the cold supply but common sense says that as the valves get old they'll start to pass water, particularly at high pressure.

You can diagnose a failed pressure vessel easily because water will spray out of the Schrader valve. Note that the pressure needs to be set with the system cold and depressurised.

Looks like the valves either end of the filling loop are not closed off properly? Also, there is caps attached to the valves for removing the hose and blanking the valves off.

Did the water run clear from the Fernox TF1? I would do the full magnet out, shut one valve, run until clean, reassemble job to eliminate a mucky drain off.

A deflated pressure vessel normally causes underpressure when the system is cold, the excess pressure when hot forces water out of the pressure release valve, then when it cools down there isn’t enough water in the system to create sufficient pressure.

A washing machine washer and a 1/2” brass cap will fit on the bottom of the TF1 as I recall to stop leaks, and should also block off the filling loop fittings.

Good luck 🙂

Thanks again for all the comments.

• I've stuck a 3/4" cap (with washer) on the bottom of the Fernox as a temp fix, that seems to be keeping the drips at bay.  I'll revisit this once the pressure issue has been solved (one thing at at time!)
• The filling loop valve on the heating side has never worked, not sure why - I should prob have insisted on a different one when it was installed.
• The filling loop valve on the cold feed side has always been fine - I'll dabble with disconnecting and capping off the other side later.  However...
• From your comments I'm suspecting the issue is likely to be with the pressure vessel - I'll check youtube for tips on rejigging it.
• No sign of the Heat Link replacement squad yet.

I had issues with my system over pressurising, was the plastic handle on the filling loop was cracked and wouldn't allow the valve to close properly.

Had to take the plastic handle off to confirm.

I had issues with my system over pressurising, was the plastic handle on the filling loop was cracked and wouldn’t allow the valve to close properly.

I once had that with the washing machine isolators, but this filling loop doesn't have handles, just screwdriver heads

There shouldn’t be any need to cap the filling loop off- the mains side has a valve and the heating side should have a double check valve (and perhaps also an isolation valve, but I don’t think yours has) so nothing should come out when the flexi pipe is disconnected.

If the mains side is leaking: there’s your problem.

A faulty pressure vessel won’t cause an increase in pressure, just an excessive pressure rise when the system is hot.

If the expansion vessel has gone or is flat the pressure will only rise when something is being heated. If the pressure keeps rising and the system is cold it's either the filling loop passing or the secondary (or 'plate') heat exchanger in the boiler pinholed. You're getting higher pressure mains water finding it's way into the lower pressure heating circuit and that can only happen in those two places, where the mains and heating circuits meet. To pump the expansion vessel up the heating system needs to be depressurised AND open to the atmosphere while you pump up the vessel. So open the TF1 for example, let the pressure out of the system, pump the vessel up to one bar while the TF1 is open, shut the TF1, repressurise the system to 1 bar, run the heating and be prepared to top it up as the boiler bleeds any air out of itself. Simples.

There shouldn’t be any need to cap the filling loop off- the mains side has a valve and the heating side should have a double check valve (and perhaps also an isolation valve, but I don’t think yours has) so nothing should come out when the flexi pipe is disconnected.

Unfortunately it seems I don't have a double-check valve.  When I disconnected the heating side, water shot out of the pipework, so I had to hurridly get the cap on there.

I did that several hours ago, however no water seems to be coming from the loose filling loop, and the pressure in the system is currently unchanged.  I'd have expected to to have increased by now, but I'll keep an eye on it.

The engineer arrived and swapped the Heat Link earlier, so it looks like it wasn't a scam after all 😀

The faulty heat link couldn't have been doing something odd to increase the pressure could it?  I'm not sure I see how tbh, but thought I might as well ask 🙂

There shouldn’t be any need to cap the filling loop off- the mains side has a valve and the heating side should have a double check valve.
<p style="text-align: left;">Incorrect, the check valves can fail quite easily, as can the cold valve. I always cap off both. They don't supply the caps with the loop kit for no reason.</p>

Left the fill loop disconnected overnight.  Pressure is normal and nothing is coming from the end of the hose...  Now totally confused 😀

I can see from the photo in the first post of this thread that the valve on the heating side of the filling loop is slightly open.

Yes, that side has never worked. It won't turn at all. Hasn't been a problem before though