Drayton MA1 mid position actuator and RTS1 room stat

22 Oct 2014
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United Kingdom
Hi all

Recently we have been noticing that every so often the radiators are very hot. On one of these occasions it turned out that the toddler had turned one of the TRV's up to 5, but on the other occasions I have been round to check all of the TRV's which have all been left set at 3. The room stat is set to 19 degree's but the ambient temperature has been more like 23 according to my thermometer. When this has happened, I have gone round and adjusted the TRV's up and down and then back to 3 in case they were somehow stuck, turned the (back)boiler off and back on again keeping the boiler stat low, checked the room stat and in general the problem seems to go away for a while and keeps re-occurring.

I now believe that the issue is either to do with a faulty room stat, or a faulty mid position valve.
I have just been looking at the actuator. when I turn the programmer from water only, to water and CH, to CH only, I'm not hearing the valve do anything. The little indicator on the side that points to either W,M,or H to show the position of the valve is missing so I cant see what position the valve is in. Other thing to note is that the casing of the pump and outgoing pipes are very hot to touch (you can touch for 1-2 seconds), not sure if this is normal.

Attached is a picture of the setup. Can anybody recommend any checks that I can do to test that the valve/actuator is operating correctly, and also how to check that the room stat is not faulty?

I appreciate any help. Thanks


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I don't think you understand how TRV's work, if the room is cold then the radiator should get hot, the number 3 is only approximate and it will turn down the water flow as the temperature is around 20°C but it could start at 19°C and finish at 21°C if your lucky, the number 3 is just a starting point, you may find for 20°C you need 2.5 or 3.5 you have to slowly over a few cold days gradually set them.

The wall mounted room thermostat should be more accurate, however it takes time for warm air from a radiator to reach the thermostat so you get a large hysteresis, every home is different with my own house with fan assisted radiators the thermostat works well because the air is moved, but in mothers house it is rather poor as there is nothing to move the air, so in the two houses the thermostats have a completely different function. In my house the wall thermostat controls room temperature, but with mothers house the wall thermostat is to turn off the boiler once the weather gets warm, it does not really control the house temperature.

There are two very different boilers, old boilers had just two modes, on or off, to control room temperature the thermostat turns the motorised on and off, and micro switches in the valve turns the boiler on and off, but the condensate boiler is very different, this boiler can alter flame height according to return water temperature, these boilers are designed to work with TRV's, as the TRV's close the by-pass allows hot water to return to boiler and the flame height goes down.

So with a condensate boiler the TRV does all the work, and the thermostat just turns off the boiler as summer approaches. However to do this the TRV and Lock Shield Valves and wall thermostat all needs to be set to work in unison.

As said each home is different there is no one method, so all I can do is say how it works with my mothers house. In the hall there is both a thermostat and a TRV on a large radiator, since the door to outside opens into this hall it needs a large radiator to reheat it fast, however once it reaches 17°C I want it to slow up heating the hall so that the main thermostat does not turn off the boiler prematurely so set at 2.75 the main thermostat is set at 18°C so it takes a lot longer to get that last degree, 18°C is low enough to ensure the house does not get too hot. As long as the doors are in the main kept closed, the other rooms can be set higher, these are all controlled by TRV's but the two down stairs rooms needs better control to that given with a simple TRV, so eTRV's used in those two rooms.

It is not perfect the best option would be to use all eTRV's connected to a central hub which in turn controls the boiler, as with EvoHome but my system works reasonably well, however it took some fine adjustment before it worked. And I don't ever now touch the hall thermostat and TRV settings, now set I leave it.
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A tip from a learned college in the combustion chamber pot, a place of great mystery, happenings & must not be entered by the faint hearted; These Drayton actuators are prone to breaking the plastic spring post & the spring will do nothing. So nothing moves or return to where it should be.

Now, IF you are competent with leccy, take the top off her & have a look.

Any advice giving is advice & not instruction.

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