Low hot pressure on tap in bathroom

[Richard Lindsay]

Hi folks,

So I have a mixer tap in my bathroom and when I move it to the hot position the water trickles out. It never gets hot, I assume because the flow is not great enough to kick the combi boiler on.

I replaced the tap thinking it was that, same problem.

If I move the tap to the middle position the water kind of fobs out (can't think of a better description). It is cold and gets faster the more i move the tap to the cold position. The only other tap in the house is in the kitchen and it is fine.

I think the hot pipe has a blockage but wanted some advice first.

Cheers for your time.

 

[terryplumb]

Something is restricting the flow to the hot tap ,if its from a combi it should virtually be at mains pressure. Any isolation valves on the supply pipe to tap ?

 

[Richard Lindsay]

Cheers for replying Terry.

Yeah, I have isolation valves on both the hot and the cold below the sink in the vanity.

 

[terryplumb]

Are they red handled gate valves ,notorious for not being fully open internally ,when you think they are.maybe not under sink but elsewhere on the supply ? What valves are they in vanity unit ,are they fully open ? You could remove tap tail from iso valve and check flow from the valve is good.

 

[Richard Lindsay]

They're compression fittings on plastic pipe with a flat head screw controlling the flow. Ive had the tap running, turned the valve off and the tap has completely stopped. When i open it again fully i get the trickle. The pipes go under the floor from there, under the kitchen and then to the boiler. I might need to just wait until we have the bathroom done later in the year to fix the issue unfortunately.

 

[terryplumb]

Up to you how to proceed Richard ,but you would appear to have a restriction on the hot supply pipework to that tap ,maybe the isolator or upstream of it.

 

[Richard Lindsay]

How would I go about testing these fittings without removing them and having no control over the water?

Cheers

 

[terryplumb]

You leave the isolator on the hot pipe ,disconnect what is connected to the isolators outlet.maybe take a pic and post here so you can be given exact instructions rather than broad brush .in a nutshell ,with tap not connected to iso valve ,its outlet side will produce a flow of water when valve is turned on .so if you connected a flexible hose to it for example. Directed to a bucket then open the valve ,you can see easily what kind of flow is coming thru the iso valve as it runs into bucket.

 

[Richard Lindsay]

Ok cheers, I'll try that tonight.

This is only testing upstream of the valve though, right?

I'd need to replace the valve to check if the valve was faulty?

 

[terryplumb]

Water coming from iso valve at a trickle ( like you get from hot tap ), would Indicate a problem with the valve ,or upstream of it. A good rate of flow from isolator would tell you that the onward pipework and tap are the issue.

 

[Richard Lindsay]

Cheers

If it's an issue with upstream of the valve, i.e in the pipe, is there anything i can do to try and unblock it without ripping the bathroom to bits and replacing it?

 

[terryplumb]

Its very unlikely that you have a blocked pipe ,not impossible ,but highly unlikely. Did original tap ever work properly ? First thing is to focus on the iso valve that you have in vanity unit and go from there.

 

[23vc]

Could it be that your tap is not suitable for low pressure systems? I've definitely seen that before where cold is mains pressure so works fine - well I've seen it on showers and pretty sure same would apply

 

[terryplumb]

Could it be that your tap is not suitable for low pressure systems? I've definitely seen that before where cold is mains pressure so works fine - well I've seen it on showers and pretty sure same would apply

He has a combi boiler 23 vc

 

[23vc]

He has a combi boiler 23 vc

totall missed that - apols