Bath hot water tap slow. Unvented system.

[kprida]

The hot tap on our bath is running slow (it was ok til recently), all other hot taps are fine. I've checked the tap over and the washer etc appears ok. I've tried a wet n dry hoover on the tap in case it was airlock (although I read this is unlikely as its an unvented system). I've poked around with a bit of wire down the pipe (couldn't get far) to see if there were any close blockages but nothing. Is there anything else I can try before I look to start dismantling pipes?

I'm guessing as its only the bath hot tap that it must be a blockage or could the check valve for this tap of gone wrong reducing the flow?


Thanks in advance.

 

[snowhead]

Flexible hose collapsed feeding the tap?

 

[kprida]

Flexible hose collapsed feeding the tap?

No flexible hose in the system, all "hard" plumbed.

 

[PlumbBobBob]

any valves? iso for instance.

 

[kprida]

All I can see is a check valve. I've tried giving it a gentle tap with the water running.

 

[jam1979]

is it defo a check valve

 

[kprida]

is it defo a check valve

Appears to be, its a mixer tap.

 

[markfxy]

Does it have an expansion vessel or air bubble in top of cylinder maybe they need recharging

 

[kprida]

Does it have an expansion vessel or air bubble in top of cylinder maybe they need recharging

It does, but all other hot taps are fine with good flow.

I did notice a small lump of what I assume to be jointing compound in the tap. Wonder if the original fitter got a bit carried away and now there's some more stuck in the pipe work/check valve.

 

[markfxy]

Bath taps need a higher flow rate might be a sign that air bubble needs topping up

 

[kozak1968]

Blockage in tap or in isolation valve (lump of scale maybe)

 

[stratplus]

Remove or change the check valve. Common problem.

 

[stratplus]

Isn't a bubble top a primatic vented cylinder??

 

[stratplus]

I guess you mean re-charging the expansion vessel.

 

[SJB6]

If all other taps on that hot water circuit are ok then the problem is the tap or the run of pipe to the tap.
Consider:
tap washer has come lose in tap valve creating a restriction in flow, have seen that many times. When you close the tap the valve will compress the washer shutting off water supply, should the washer have come lose then it will be flapping about in the bottom of the valve creating a restriction.
Also consider that like you said a previous plumber got carried away with jointing compound and seeing as jointing compound, plumbers mate, silicone etc etc is designed to stop water then if there was any remaining in pipe work it will cause a restriction in flow. I personally have found foam lagging in the bottom of a hot bath tap before causing a restrition. The plumber who changed the hot water cylinder cut too much foam lagging from the cylinder when installing brass connections and some got caught in the system.
Also like a previous plumber pointed out, if your in a hard water area then scale deposits could cause the same problem.

 

[Whyme]

Isn't a bubble top a primatic vented cylinder??

nope. a megaflo or similar unveted cylinder has a bubble or chamber of air that takes the expansion rather than a vessal. a primatic is open vented and has a chamber but doesnt mix the hw and ch ( it only has 1 f+e tank)

 

[SJB6]

Yes I should have pointed that out. Like Whyme said unvented cylinders utalise either an inline expansion vessel or a built in air gap within the cylinder itself. An expansion vessel that had lost its charge or an unvented cylinder with an airgap malfunction ie. gone and air escaped through pipework would not alter the pressure of water at taps an certainly not just one, only faulty temperature mixing valves found with pressurised hot water circuits could cause similar problems. A Primatic like he said as well is an open vented system, there is an internal air gap within in the cylinder which accomodates the expansion of the water in the heating circuit, there is one header tank/feed and expansion tank for the hot water cylinder and the heating circuit fills from tha as well, should you lose the air gap in the cylinder then draining down the cylinder and re-filling is the only way to return the air gap, but like i said this is not a cylinder issue wever its unvented or open vented.

 

[tamz]

If you can afford £50 - 70 quid on the right plumber it is a no brainer one call fix. Sometimes you just need to call in a pro.

 

[SJB6]

Yes one call is all it takes.

 

[stratplus]

Thanks for that, never realised some unvented used a similar system to the primatic open vent!

 

[SJB6]

Thats ok. Primatic cylinders have been around for a very long time though and I have only ever come across one in my time, despite the many, many houses, mansions and caravan home sites i've been called to, most primatics will have been updated to newer systems a long time ago.