One for the plumbers

[John]

Not DIY (but could be given the right guidance). I have a house that I rent out to tenants. They are telling me that the CH doesn't work properly. I have been and had a look and the scenario is this. The boiler works fine and fires up etc. but only when asking to heat the water (stored not instantaneous). When the boiler is heating the water the rads also get warm (not red hot). When the water is up to temp the boiler then shuts down and the rads cool down. As the domestic water is up to temp the boiler cannot be fired up, either automattically or manually, to heat the rads until the hot water either cools naturally or some is drawn off so allowing new cold water into the tank and cooling down that way. The room thermostat is turned right up to 30 degrees and the cylinder stat is at approx 65 degrees. I realise it is a "How long is a piece of string" question but any ideas what the possible cause is and how much it would cost to fix? My thought are leaning towards the motorised valve in the cylinder cupboard been cattled as I seem to remeber reading about something similar in the past.

Cheers

John

[Ret.]

I would suggest that as the most obvious cause. I've recently switched to a combi - but my old system had two motorised valves - one controlled by the cylinder stat and one by the room stat. If you can see the valve(s) you can check if they are working by getting someone to turn the stats up and down and watching to see if the lever(s) on the motorised valve(s) moves.

Ret.

[Muddymike]

You can also hear them operating when a thermostat clicks in. Could also be the pump of course.

Mike

[Slider]

Probably the synchron motor in the motorised valve. You can buy from Screwfix for about £14 and fit in 5 mins. As a stop gap to get them warm.

Turn the thermostat on the hot water cylinder to maximum. Turn the thermostat on the cylinder to low Set the motorised valve to manual.

[robgraham]

Having looked at the replies, my logic says that the room thermostat is cuffed or the wiring to it has become faulty.

If the thermostat was OK, then the boiler would fire and if a valve problem would shut down when it tripped it's overheat sensor.

Is the pump running - presumably the thinking is yes as the radiators are getting some heat and the tank a full whack.

Rob

[Slider]

No, because you have turned the thermostat on the boiler to minimum, it will never heat the water enough to achieve 90 deg

Do you not have a thermostat on the boiler itself?

Yes

[John]

OK but wont that make the hot water too hot to use safely as it goes up to

90 degrees

Don't understand this, I only have one stat on the cylinder

By moving the lever?

Cheers

John

[BigWallop]

I'll second this.

Firstly, find the motorised zone valves. They look like rectangular metal boxes on the pipework, somewhere between the pump and the hot water tank / radiators.

With the system turned on, feel if the levers on the valves are easy to move. If one of them is tight to move, then it sounds like that is the valve that has a fault. Try opening it manually to see if the radiators heat up. The lever will lock open if you latch it on the little metal tag on the valve head casing.

Make sure that all timer systems are also working properly. The switchgear in the timer units can also go faulty, and this type of fault is better tackled by an engineer with the correct test skills. Unless you know a bit about electrics? If you do, then get back to us, and someone will talk you through the process.

But try the valves first, and you might just get your tenants a warm house for the evening, until you get a permanent fix.

Good luck with it.

[Tim Downie]

Go back and read your own post Slider, that's not what you said. You said "cyl>

No doubt not what you meant to write but what you said was confusing.

Tim

[John]

Thanks for all the replies guys. I think (hope) I have fixed it. I went round (2 mins walk) as they were saying it wouldn't come on at all now. I moved the lever on the valve back and forth a few times and it fired up as 'normal'. The tenant has just called to says thanks and that the rads are red hot!! The Landlords Gas Check is due in the next week or so, I will get the guy to give it a check when he goes for that.

Thanks again.

John (and tenants)

[Roger Mills]

It's almost certainly a motorised valve problem, and the OP's later post seems to confirm this.

I guess it's a Y-Plan system with a single 3-port mid-position valve. If these stick in the mid position, the boiler fires via the cylinder stat and heats both the HW and the CH. But once the HW demand is satisfied, the boiler and pump go off and only come on again if the valve moves all the way to the CH-only position - causing a micro-switch in the actuator to close. It can't do this if it's stuck.

[YAPH]

Had one just like this the other day. The 3-port valve was correctly going to the CH position when the thermostat and programmer told it to (or to the mid position when HW was also being asked for) but the boiler would only actually fire up when HW was called for (i.e. motorised valve in the mid-position). Looked like a problem with one of the microswitches in he valve head. Replaced head, problem solved.

[Slider]

Apologies. Cylinder stat to maximum, BOILER stat to minimum