Combi boiler - central heating fine, kitchen tap fine, bath not fine

[HereditaryTools]

Having some issues with hot water in our flat and hoping that people might be able to help us isolate what and where the problem is.

We have a Worcester Greenstar combi boiler - either the 24i junior or the 28i (I should know which but there is nothing anywhere on the casing to indicate.) About 9 years old (installed by the previous owners).

Although we have had some issues in the past with hot water, this has usually been resolved by re-pressurising. We have typically been able to run hot, deep baths quite quickly with this boiler, so I don't think it is underpowered for our needs. All was working fine until a couple of weeks ago, but now the hot water in the bathroom has slowed to a trickle.

The central heating is fine and the hot water tap in the kitchen (right next to the bathroom) is fine - normal flow and as scaldingly hot as ever. The pressure also appears to be fine this time. When I turn on the hot water tap in the kitchen, the boiler fires up immediately. However, when I run the hot tap in the bathroom, the boiler either does not start up at all or takes a long time to do so.

If I run the hot tap in the bathroom, I get a normal stream of cold water (although possibly less flow than there used to be). When the water starts to heat up, the water drops to a tiny trickle. If I turn the tap halfway off, I get slightly more hot water, but still only a small stream. This lasts for maybe 2-5 minutes (not quite enough to cover the bottom of the bath), then it goes cold and I get a gush of cold water (again at nearly normal rate).

The tap then runs cold for maybe 10 minutes, before going back to a wee trickle of hot and then back to cold. Sometimes it never gets hot no matter how long the tap runs. Meanwhile, the boiler goes on and off, seemingly unrelated to whether there is hot water or not.

Any ideas? Is it more likely to be a problem with the plumbing in the bathroom, or could there be a problem with the boiler that only affects the bathroom hot water supply? Let me know if I can give any more useful information. If it helps, we live in London, with very very hard water so limescale might be causing an issue in on or more places.

Calling in a plumber is difficult at the moment, but if you can suggest anything that two laypeople could try to fix this, that would be hugely appreciated.

Many thanks...

 

[Heatfix]

Is it a single hot tap or a thermostatic mixer?
Most likely if its a hot tap then the washer or or gland is faulty and needs replacing. Shouldnt be an issue with your boiler as the other hot taps work fine.

 

[Agile]

It certainly sounds like an issue with the bath hot tap.

Perhaps open it and inspect the inside.

Having a replacement washer would be sensible.

Tony

 

[dilalio]

See if you can get hold of a manual for the tap in the bathroom... Is the wash hand basin in the bathroom ok?
First check if you have an indice in the spout of the bath tap that unscrews (with spanner) and check that there is no blockage to the strainer/mesh. If that's clear or there isn't one then isolate incoming water main and dismantle hot tap body and check for debris, washers etc.
If it's a mixer tap then cartridges may need cleaning/replacing.
Take them along to your local trade counter (before 1pm on Saturdays) and ask them to help identify what you need.

 

[HereditaryTools]

DID IT!!

Thanks to everyone for their replies. It is a very old-style mixer tap - the bathroom is the one part of the flat that has never been updated, and everything is unbranded, probably cheap and dodgy plumbing installed with all kinds of bad practice. We haven't lived here many years, so any instruction manual or useful info about the components are long gone.

Decided to open things up to take a look. No way to isolate that one tap - no in-line valves or anything, so had to find the main stopcock (should have known about this but never needed it before). That was jammed shut, but eventually got it moving with WD40 and some cautious wrenching. Will keep it oiled and moving from now on.

Undoing the tap valve was a major PITA - I don't think it has been touched since the bath was installed in about 1980. Again, tried WD40, then bought a newer, better wrench (Bahco), then tried heating it with a hairdryer and eventually it submitted.

The washer looks fine, but when I took the valve all apart, there was some gunk inside. Also some limescale in various places. Cleaned this up as best I could with limescale remover (hope this is okay on brass), washed it all out, dried it and put it back together. Instant hot water. Lots of it. Bliss.

I would have just replaced the valve, but the old ones seem to have a weird obsolete number of splines - and the head carriers for the tap handles are designed to fit those. We would have to replace all the tap handles as well, to fit on on normal valves with a normal number of splines. Basically, we need a whole new bathroom, but can't afford it just yet, so we are keeping the old stuff on life support.

For an encore, I am going to try to mend the handle of the basin tap and fit a new toilet seat. I have some new toys, and I have learned some important new things, so all is good. I may be slightly high on WD40, though. Many thanks again for supporting a plumbing newbie.

 

[dilalio]