DHW Cylinder Thermostatic Valve ????

grib · 17 Oct 2007

I feel a bit of a dummy for asking but in 12 years servicing heating systems I've never come accross one of these (with a problem)

I have a customer who has a Thermostatic valve fitted to the flow of his gravity hot water system...

He's only getting luke warm water and I found there is very little circulation to the tank unless I crank the boiler up to max and then it will circulate so I'm guessing the valve is partially stuck.

I've taken the top off and found the needle very stiff. With radiator valves the needle will spring up when pushed down and I assume these work in the same way...however I was once told never to assume anything which is why I'm asking the question

The needle on this valve (Drayton) won't spring up if pushed down... I can pull it up a little but it will not spring up on it's own and even when I physically pull it up the flow is minimal.

1. Does this sound like it's faulty.....
2. Are they repairable if I strip it down...or is it a straight forward replacement.

Cheers

cozzmic · 17 Oct 2007

Tap the end of the pin with a grips or hammer,(quite firmly) it'll be the seating stuck in the valve if it don't work Danfoss did one called a VMT which fitted on the return and a sensor on the HWC.

Biggles.. · 17 Oct 2007

Drayton still make them, looks like a TRV4 but is inline.

grib · 17 Oct 2007

Thanks guy's... the top does look exactly like the TRV 4 and it is inline but on 28mm...

I gather from what your saying the pin should move exactly the same way as a rad valve (which is what I thought but just wanted to check). I got about 2 to 3 mm movement upwards on the pin if I pull it.

I did tap it downwards a few times but I wasn't too heavy handed so I will try with a hammer. If that doesn't work is it worth draning down and taking it apart... I'd rather fix it than replace it if possible, but don't want to drain down twice if I can avoid it.

Biggles.. · 17 Oct 2007

To be honest rather than keep messing about and end up with it sticking again i'd replace it.

grib · 17 Oct 2007

Any ideas on a part/model number I've searched all over and can't find it. I've been through the search on Plumb Center (so called because it's run by plums I think) and nothing comes up...been to draytons website and can't find anything even tried googling "Drayton 28mm inline thermostatic valve" and nothing ??

Biggles.. · 17 Oct 2007

drayton 2 way tap stats are what you want. the new version comes with some capillary tubes, this is from memory so might be way out.

JohnD · 17 Oct 2007

A similar thing used to be called a Cyltrol Valve, I believe they are still sold (from "Cylinder Control" i suppose).

edited: see http://www.invensyscontrolseurope.c...es/Drayton/Nonelectroniccylindercontrols/[/i] about £70

BTW does yours have a splined spindle with a plastic knob? How does one get a new knob when the splines have worn on the old one?

grib · 17 Oct 2007

lcgs said:
drayton 2 way tap stats are what you want. the new version comes with some capillary tubes, this is from memory so might be way out.

You are my hero.. I googled "drayton 2 way tap stats " and found it striaght away !!! easy when you know what somethings called

bripl · 17 Oct 2007

there are several names/types of them
danfoss kov
drayton tap stat[2 port/3 port]
myson tcv

plumb centre stock the drayton and myson but you have to be patient

grib · 17 Oct 2007

bripl said:
plumb centre stock the drayton and myson but you have to be patient

It took them two weeks to get me a stelrad radiator, God only knows how long something like this would take...... Mind you they probably make me wait deliberately because I keep telling them I can buy stuff cheaper from screwfix than I can from my TRADE account ...... and if there's more than two people in front of you at the counter it's probably quicker to get it delivered by screwfix too !!!!!

gas4you · 17 Oct 2007

Didn't realise you're in Norfolk.

You aren't refering to the Hellesdon branch by any chance?

grib · 17 Oct 2007

gas4you said:
Didn't realise you're in Norfolk.

You aren't refering to the Hellesdon branch by any chance?

No I'm a bit further south than that... almost into Suffolk... but I think it's standard training for all branches.... I'm not going to mention where I am incase they read this forum and blacklist me !

Biggles.. · 17 Oct 2007

Our plumbs if held on feeder is next day before 10, no more than 3 days from manufacturer or stock transfer takes 2 days.

The one we're using in Scunthorpe never has anything we ask for and just presumes we're making items up cos they dont stock them.

Onetap · 18 Oct 2007

You could replace it, but the big disadvantage with them is that they do not interlock with the boiler, i.e. when the DHW cylinder is up to temperature, the boiler will continue to fire.

The pump (assuming it's not gravity) will also be running when the thermostatic valve has shut off the flow path; this doesn't do the pump any good and increases the risk of pumping over. The thermostatic valves were OK for solid fuel fired boilers with gravity circulation, but they are 50 years out of date now.

You'd do better, to replace the 2-port thermostatic valve with a clamp-on thermostat and a 2-port zone valve, so the end switch would switch the boiler and pump on/off. Wiring diagrams are to be found on the Honeywell site. It would save the customer a lot of fuel, as well.

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DHW Cylinder Thermostatic Valve ????

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