When only the HW is on, the radiator closest to the HW cylinder heats up. I have a traditional standard HW cylinder with 3 way valve. Is it likely the 3 way valve is faulty? Would the 3 way valve be faulty or could it be the 3 way valve has been wired incorrectly? Or could there be another reason?
I have recently moved into this house so unfortunately, do not know the history of this fault.
Some Honeywell TRV's in the house (prob 10 years old) are off when switched to '0' (normal I know), but when turned slighty towards '1' then hot water flows into rad. The room temp is around 18 Deg. Is this normal functioning of a TRV? I thought they would only open if room colder than temp setting on TRV? I assume setting '1' is below 18 Deg.
It is quite common for one radiator (often the bathroom one) to be arranged as a bypass for the boiler. This is so that if the room thermostat turns off and the boiler is firing, the excess heat can be dumped by keeping the pump running (over-run) rather than letting the boiler boil the water, which is what would otherwise happen with older boilers.
If you don't like it, dependning on the boiler, a bypass using an automatic valve could be fitted (typically near the 3way valve to provide this.
The numbers are not really that accurate. You can test for proper operation by increasing the setting and letting the room warm up and seeing if the radiator starts to cool down then. TRVs work by the expansion of a wax element normally, and are not on/off devices, but rather close down the flow as the room warms.
After 10 years, it's entirely possible that the valve head has work out (7 years is claimed to be the average), or that the the valve mechanism is stuck with the pin underneath not moving (not in this case).
It's probably worth going round and checking all the TRVs and replacing any that are dodgy.
The hot water flows into a bedroom rad (next to cylinder). If hot water also flows into bathroom towel rail and eventually the next bedroom would this mean more than just a bypass? Would this then be a valve problem or just a big bypass?
I apologise, but just to get my head around these TRV's once and for all, should any hot water at all flow into the rad if the TRV is set to the 'frost' position and room temp 16-18 deg? They turn off the hot water flow at '0' but let hot water in after a very small turn of the TRV.
In that case, it is common that the towel rail is being used as a bypass and would be heating up equally regardless of whether CH or HW is on. If you have a way to trace the pipes, you could prove this because the connection for the towel rail will be before the valve - i.e. on the boiler side.
Ignoring the TRV issue for a moment, if the bedroom radiator is warming up when only the HW is on then I can think of three possible reasons:
- It is connected to do that - i.e. arranged as part of the bypass. This could simply be that whoever installed the system found it easier with the plumbing (because they were together on the same pipe branch) to make both the bypass. Probably more true if the bypass was organised later, perhaps because the boiler was making bumping noises (boiling basically) at the end of a firing when the thermostat had gone off. Again you'd have to trace the pipes.
- That there's a problem with the diverter valve letting some water into the CH side when it is supposed to be on HW. This can be because the paddle or ball inside is worn out or because the system has sludge in it, around the paddle or ball. You can test this idea by feeling the pipes around the valve - if it's letting by, it will be warm. Solution is to clean up system/replace valve or both.
- That the return pipes from the CH are not meeting together before joining the return from the cylinder - i.e. some radiator returns are connected on the boiler side of where the HW return joins and some on the other In this case it is possible for a circulation path to be set up through nearby radiators when just the HW. This one is easy to diagnose because the ends of the radiators that are normally the cooler will become warm. Probably the radiators won't get as warm as normal.
All of the above assume that the TRVs are open to some extent.
The second two should be fixed if they are happening - the first is up to you.
On the Frost setting, I would expect the flow to be off at that temperature. It either means that the valve head is knackered or the base is gummed up and not moving. You can try removing the head and pushing the pin underneath a few times to see what happens. It only moves a few mm though. If inconclusive it's best to replace the valve entirely. Since you would have to drain the system to change the bases, it would then make sense to give the system a thorough clean and change all of them while you're at it, not forgetting to add inhibitor afterwards of course.
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