Bath hot tap doesn't get as hot as other taps

Participant · 24 Mar 2013 at 12:18

Hi all

Grateful if you could help me troubleshoot this weird problem I've got please.

Basically, the hot tap for the bath in the main family bathroom only ever gets moderately warm. No other tap in the house has this problem, so I'm fairly sure it's not a boiler problem. The boiler works fine otherwise. The sink in the bathroom gets hot no problem.

It seems to be pointing to a faulty tap mixer, but I don't want to replace it before I'm sure that's the thing. Must be that though, right?

Ps the hot water comes directly from the boiler ie there's no hot water tank.

arknor · 24 Mar 2013 at 12:38

probably a thermostatic mixer that has possibly failed.
thermostatic only let the water mix to around 40c or something crappy like that though

a lot of them use a crappy wax element that are prone to fail

Glaucus · 24 Mar 2013 at 12:57

As above most likely one of those stupid pre mixing taps, to ensure dumb people don't get burnt and often mix to cold by design.

Nightglow · 24 Mar 2013 at 14:30

Robbie: Has it always been like this or as the problem just started?

You can adjust the temperature on a lot of thermostatic bath mixers.

Participant · 24 Mar 2013 at 14:46

Thanks guys.

The problem's been there ever since we moved into the house in December. It's hot enough (just) for a bath for the little one, so it's been low down my list of priorities. Looking at getting it sorted now though.

I'll have a look at it and if there's no adjustment or obvious resolution, I'll just replace it with one fro Screwfix.

Nightglow · 24 Mar 2013 at 14:53

You can remove the screw & handle, & it could be possible to adjust the temperature.
Most can be adjusted the same way, like the one in the links.

http://www.youtube.com/watch?v=1FP4LCgQGtE

http://www.youtube.com/watch?v=PCYper2DpG4

Participant · 24 Mar 2013 at 16:16

Just been up to have a look. I don't think there is a thermostatic adjustment:

However I did discover something...when I turn the cold tap very tightly off with all my strength, the hot tap runs very hot as it should. Therefore I'm guessing that I actually have a cold tap problem.

Is this likely to be serviceable, and if so, how? Annoyingly they don't seem to have put isolation taps / valves on the pipes.

Thanks a lot for the help so far!

arknor · 24 Mar 2013 at 16:25

maybe the rubber washer in the cold tap needs replacing if that's the case

Nightglow · 24 Mar 2013 at 16:35

That tap is not a thermostatic type, just a plain bath mixer.

With my boiler, I just switch it off, & turn off the stop c ock for the cold water.

That should stop the hot & cold water to the taps, you can remove the brass part, usually a rubber washer to replace, might be a ceramic disc, but looking at the tap I doubt. Easy job to do yourself.

But, if you have to use so much force, then the tap might need reseating to allow the washer to sit correctly, so it's then cheaper to fit a new mixer tap.

A lot of mixer taps now use a ceramic disc instead of a rubber washer, & only need a quarter turn to turn them fully on.

Participant · 24 Mar 2013 at 17:11

Cheers guys. We're just going to replace it as we fancy a shower mixer on the tap too.

At least we know it's not faulty pipework or a problem with the boiler!

Orionaut · 24 Mar 2013 at 17:16

You get more water flow through bath taps than basin ones. If you are using a combination boiler/Geyser then the higher water flow might be overwhelming the boilers ability to bring the water up to the desired temperature.

Try only tuning the tap on slightly so that the water flow is the same as it would be from your other taps. Is the water still cold??

If under these circumstances the water is now hot then you have your problem! you will just have to run the bath slowly. (Or fit a more powerful boiler)

If the water is cold at all flow rates then you have something weird going on!

Participant · 24 Mar 2013 at 17:25

I've found the problem and posted it already

. The boiler is fine, the kitchen tap chucks out hot water at a hell of a lick. It was the fact that the mixer was drawing in cold water even when closed.

Nightglow · 24 Mar 2013 at 17:49

Robbie G said:
Cheers guys. We're just going to replace it as we fancy a shower mixer on the tap too.

Suggest you get a Thermostatic Bath shower mixer, safer to use especially you got kids, gives you temperature stability if someone turns a tap on elsewhere in the house.

Participant · 24 Mar 2013 at 20:49

Sounds like a good idea. Going to go to Screwfix tomorrow and pick one up.

Participant · 25 Mar 2013 at 23:15

Well I fitted the replacement tap, and I think I need to go cap in hand to orionaut, because I in fact still have the problem that the hot water tap in the bath doesn't produce really hot water until I dial back the flow slightly on the hot tap.

It's the only tap that's served by 22mm pipe in the house as far as I can see, so I think the extra flow is just too much for the boiler, which is a cheapy Ravenheat csi120. So unless there's an actual fault with the boiler, we're just going to put up with it until we can justify a replacement boiler or an unvented cylinder. It still chucks out hot water at a decent lick and the shower off the mixer tap is a million times better than the crappy electric on the wall, so maybe in a few years we'll look at a 50kW Worcester Bosch or something.

I've read about water / water heat exchangers getting gammed up, but tbh with this cold weather, I reckon my boiler just isn't man enough to provide a high enough rise at full flow.