I made the mistake of buying a Triton Altair thermostatic mixer 9 months ago - a special offer from Screwfix - quite cheap. It has started only providing hot water or cold water but nothing in between. I realise you get what you pay for, and would much appreciate people's recommendations for a good quality, but good value, thermostatic shower mixer - surface mounted.
TIA
Keith
Well I got a triton tyne mixer, looks like a different design to the altair to me, its the "unichrome" range. Its been fine for 2 years so far. But you may have been put off triton now ! If its faulty inside a year, can't you return it ? Simon.
Yes, not sure what guarantee arrangements are with Screwfix - am getting in touch, but I thought it might be useful to see other's comments anyway.
Keith
All shower valves pack up eventually. Not sure what design yours is but the bar mixer valves have the tremendous advantage of ubiquity: everyone and their dog makes them. Admittedly some /are/ dogs, but no matter because they're a doddle to replace when the time comes (isolate water, undo two nuts, swap valve, do up nuts, water back on)
Installed a Gainsborough, probably 7+ years ago, and have been very pleased with it. It was an obsolete model at the time, so I got it very cheap, but it was originally very expensive. I flush fitted it, but it also came with surface mounting bits.
Note that there are different types.
For the thermostatic part, the cheaper ones use slow acting wax actuators, and the more expensive ones use what look like bi- metalic springs which are very fast acting -- generally fast enough to stop you getting burned (or even noticing) if someone else suddenly opens another cold tap, and these should be used with any form of instant multipoint water heating (including combis).
There's also the issue of input pressure. My Gainsborough came in 3 versions to handle 3 variants. Mine is for high pressure cold and widely varying pressure hot, and is intended for combi and multipoint use. Another version was low pressure hot and cold (e.g. header tank), and I think the third was probably high pressure cold and low pressure hot. Two of them can be easily converted, but the third can't.
Some of the cheap bar ones are completely useless with instant water heating, because they try to reduce temperature by reducing the hot flow rate. Most instant water heaters increase the temperature as the flow drops, because they are operating in constant power mode. So the shower output gets hotter as it is being fed constant power but the total flow is being reduced, which is the opposite of what the mixer is trying to do. If you have a combi or a multipoint, make sure you buy a mixer designed for operating on one.
I have never seemed to get on with thermostatic showers, even the expensive Grohe one at my Uncles house.
I find that the slower response of the wax capsule type in my own bar mixer valve is not an issue: when someone turns on the hot water at the kitchen sink and the supply of hot water drops, which would result in a huge drop of temperature on a non-thermostatic mixer, there is a momentary drop of temperature which is noticeable but not uncomfortable while the thermostatic element adjusts the mix. (And of course a reduced flow while the other tap is also running.) When the other tap is shut off there is a corresponding brief, noticeable but not uncomfortable, rise in temperature while the mixer re-adjusts.
I'd agree that the Mira/Aqualisa bi-metallic type are probably the Rolls-Royce of mechanical mixers, but a replacement mixer element for one of those costs more than a whole bar mixer valve, riser rail hose and head!
Of course if you're mixing down from pathologically hot sources like hospital supplies or unregulated, maybe solid-fuel-fired stored hot water systems then you really do need TMV 2 or 3 (not sure which applies) certified mixers to assure safe temperatures.
They all - from LiDL specials to Hansgrohe - reduce the hot flow rate to reduce the temperature. What else can they do? Series regulation rather than shunt regulation if you like. (S'pose they could dump excess hot water to drain but it'd be a bit of a waste of water and energy!) Or am I'm missing your point Andrew?
Increase the cold flow rate?
I fitted a pressure balancing valve before my thermostatic wax type mixer, to get the best of both worlds. Seems very effective. Simon.
Yes.
Actually, if it knows its running from a constant power heat source like a maxed-out combi or multipoint heater, it can reduce the temperature by increasing the hot flow, but I don't think they do that.
But this strange non-obvious and contrary behaviour is why showers which aren't designed for combis/multipoints don't work very well with them.
My Gainsborough seems to have another check built-in. If I turn off the cold water supply, it won't let any hot water through either. When I first found this, I thought it was broken, but it seems to be by design, presumably to prevent scalding if the cold supply fails.
Isn't that expected behaviour from any thermostatic valve? Temperature of hot supply above demand temp => valve shuts down hot inlet to try to acheive demand temp; no cold supply? => no output.
Sounds like a pressure equalising valve operating.
I fitted a pressure balancing valve before my thermostatic wax type mixer, to get the best of both worlds. Seems very effective. Simon.
It does it even if the hot supply isn't actually hot, and without running any water to actually see.
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