Central heating weirdness

Help! My central heating has gone strange – basically, it now only heats upstairs. Downstairs (where the thermostat is) is freeizng, radiators not on. Boiler fires up, goes for a couple of mins, then off. I have no clue! It seems to coincide with me turning on the spare room rad, which has been off for about a year, cos my brother is using my house next weekend. But why would turning on one upstairs rad, turn off all the downstairs ones??

Are they on separate circuits? Could be the valve that switches between (name completely forgotten)

could be an air lock?  air in the unused rad getting into the rest of the system?  Just a guess

Do you have trvs on your rad? Are they turned off?

I would turn the boiler onto continuous, set the therm to 24°c and go from one rad to the next. Check the pipes entering each rad and see if the feed pipe is warm. If the boiler goes off after a few minutes it would suggest the thermostat thinks you house is warm enough.

Zone valve jammed off.

Don’t know your set up but not uncommon to have upstairs downstairs zones via a valve.

+1 for zone valves.

if the servo has failed the valve will be opening.

They normally have a slider to open and lock open manually try that.

Bleed your radiators and top up the water in the system.

brill, thanks folks. I don’t know answers to any of the questions! But a bleed sounds fair (youtube me up!)

Where should I start with the bleed? Boiler is old school, not combi, and is downstairs in the kitchen

They normally have a slider to open and lock open manually try that.

I dunno where to look for this 🙁

Without knowing your system and indeed if in zones, turn all the radiators off. Bleed each one. Turn on one downstairs radiator and turn on heating, then check for heat. If heat in radiator, open next one downstairs, and continue, then start with upstairs. This can move an airlock. Then bleed the radiators.  We usually have one radiator that get’s air in, so only bleed the one radiator.

look near the boiler or tank or in cupboards that are dusty and you may see one of these

https://www.unventedcomponentseurope.com/honeywell-2-port-motorised-zone-valve-22mm-v4043h1056.html/

the slidey metal thing beneath the wire is the manual over-ride – slide it across (it will make a servo sound) and lock it in place above the notch to test. If that makes a difference it needs replacing (realistically by a plumber) – they do fail

I thought zone valve too.

If you can find them (ours are adjacent to the tank) they’ll look like little grey/silver boxes with an electric lead going in. When the heating switches on you should hear the motor turning for a couple of seconds. It could be that one of them is stuck, in which case you may be able to open it with a little lever sticking through the case.

They’re not expensive or time consuming to replace.

Excellent, thanks. now I’ve fixed my fence, have some more fun stuff to get on with 🙂

Help much appreciated

Maybe a dumb comment/question, but if there’s two zones, wouldn’t there be a thermostat upstairs as well?

If it is the zone valve that’s not working it’s almost always the motor, replacement is pretty straightforward as long as access is ok. https://www.toolstation.com/thermocouple-synchronmotor-synchron-motor-240v/p27779

After you have bled them, balance them.

Can you clarify. The boiler fires for 3 or 4 mins , enough to generate some heat then the boiler switches itself off?

Because that’s sounding like a safety control possibly overheat.

Stuck valve? Recently our heating wouldn’t switch off and it ended up blowing the control board in the boiler. I wasn’t in so no one did the obviously of powering everything down once it became obvious that neither the control panel or thermostat were doing anything. Basically ended up with an overheated boiler. When I tried manually to move the motorised valve manually it was obvious it was seized. Luckily my next door neighbour is a plumber and boiler engineer so got it fixed very quickly

Lever on side  of 2 way valve , usually black .

Will move with resistance and a feeling of operating a highly geared ratchet.

3 way control don’t always have these.  However a stuck valve on some boilers is a no go , boiler won’t fire

If it’s a stuck valve you might get a replacement off the shelf at Screwfix

Bleed each one. Turn on one downstairs radiator and turn on heating, then check for heat.

Before messing with valves I’d be doing what Fossy said – nicely non-invasive!

Doesn’t make sense that a valve should fail just by opening an unused rad – could be an air lock caused by air from that rad though.

The boiler fires for 3 or 4 mins , enough to generate some heat then the boiler switches itself off?

Because that’s sounding like a safety control possibly overheat.

Yes, possibly that. Not had a chance to mess with it yet, but opened the airing cupboard to look for the valve and its very hot in there.. think that black lever on the valve is in there. will post pic

How’s the hot water? Anything funny going on there?

Hot water seems ok.

Just bled all the rads… one I realise after I hadn’t turned off, but everything’s the same after turning heating back on and opening a downstairs rad. No noise of it filling/heating up. Boiler fired up and went off again, so that safety/overheat is a definite possibility. Just gonna have to get a man in, I’m too useless to sort this out.

These are the boxes on the pipes in the airing cupboard

has WMH down the left side with the switch (which doesn’t budge) on H

and this, the white thing turns anti-clockwise 90deg

Boiler shutting down sounds like low pressure. Can you see the pressure reading on the boiler?  Could be caused by opening up a dormant radiator I guess.

If it is low pressure it is usually easily sorted especially if your boiler has a built in fill loop.

check the boiler model number and YouTube for a guide.

Nope, all I can see is the pilot light hole and the on off dial, this boiler is so old, don’t think it has a pressure gauge. It’s one of these –

.https://youtu.be/ueXdC3qlXuI?t=33&si=QSx4QlDdenJmJd65

Will get man in next week and look to getting it replaced.

These are the boxes on the pipes in the airing cupboard

The first one may well be the motorised valve for the hot water (the cable would probably go to the thermostat on the cylinder and/or to your CH programmer).

The red one looks like the CH pump.  Make sure that is running – you can usually feel a slight vibration when it is.

I still think* it’s an air lock causing the CH water to not circulate properly resulting in the boiler overheat cutting in.

Air locks can be an utter PITA.

If you switch off the CH but run the boiler for HW only does it still trip out?

* I’m def not expert but I’m old and tight so they to fix stuff myself.

Y plan system I think looking at the pictures.

Suspect the 3 position valve is stuck. Hence why it overheats and switch itself off , and you can’t move the lever.

You could try popping the grey cover off , it’s live so isolate it first. Pull out the motor and see if a set of adjustable spanners will move the valve . However , even if you get it moving there’s still the possibility the synchro motor has burnt out.

Ianap so might be wrong.

Weird how it seemed ok though and opened up the rad borked it . So it could be crud in the valve port .

Thanks mate 🙂 Will have a look at that

From your poor description, it sounds like the thermostat is calling for heat, the valve opens, the boiler fires up, runs for 3 or 4 minutes, then turns off.
That points to the boiler flow temperature sensor reaching its set point, then turning off the boiler. It will take a while for it to cool down enough, and restart the cycle.
If the valve or motor were faulty, it would not fire the boiler. Same with the thermostat.
Some of the rads are getting warm due to gravity water feed, where the hot water is exapnding, going up the pipes and pushing the colder water down, just like hot water systems were 20+ years ago.

The first thing I’d be looking at is the pump. If the pump isnt working, this is exactly the symptoms I’d expect.

On the front of the pump, where all the model numbers and printed writing is, there is a largish (20mm) screw, that can be undone with a flat head screwdriver. Take this screw off, and see if the shaft is turning when the boiler is on. There will be a small amount of water coming out when you do this, so get a jug or towel handy. If the shaft behind the screw cap is not turning, try and turn it with a suitable screwdriver, they do partially seize up, and using the screwdriver on the shaft can be enough to free them. If that doesnt work, and you know you have voltage to the pump, then it is a faulty pump and will need replacing. From the limited pic you put up, it looks old, so it has quite possibly failed. Also, the internal impellers sometime break up, so the pump can still appear to be turning, but its only the shaft turning, the impeller has come off or broken.
Either way, pump first to check you have circulation.

You could try popping the grey cover off , it’s live so isolate it first. Pull out the motor and see if a set of adjustable spanners will move the valve . However , even if you get it moving there’s still the possibility the synchro motor has burnt out

The whole actuator (MA1) lifts off the 3-way valve without having to disturb any of the electrics, that tab on the right is a quick release. Push it in, pop off the plastic box and you’ll see the spindle the synchronous motor moves and you can turn that as required. If that get a flow going through the heating circuit then I’d suspect the actuator has failed, though it’s probably just the synchronous motor that’s gone.

£20 for a new motor, £60ish for a whole new actuator including the motor. Amazon will do the actuator complete with valve for £61 which seems bizarre to me but you can just use the actuator and keep the valve as a spare, though tbh they rarely give problems unless you’re in a hard water area or run the system without an inhibitor. Either way there’ll be some mains off wiring to do but it’s easy stuff, no plumbing involved.

Either way, pump first to check you have circulation

If the hot water is working the pump’s fine.

If the hot water is working the pump’s fine.

Possibly, but a dead pump can allow enough gravity fed water through it even when not turning to heat the cylinder. It doesnt take a great deal of force to run through the pump impeller.
But yes, it could also be the motorised valve, that is stuck in the HW position, but then some of the rads are getting warm, so at worst its in mid-position, if so, the HW will be getting hotter than normal, as the valve wont shut when it gets to temperature – but then why do only half the rads, those upstairs, get warm – possibly gravity fed getting to the warm rads, as if in the misposition, it should be giving heated water to both circuits, and both up/down rads and HW will be getting the heated water from the boiler.
Pump would still be my first check, then I’d be getting the meter out to see what power the valve is getting, if that isnt clear, the temperature clamps would be out to see where the water is flowing.

Pump would still be my first check, then I’d be getting the meter out to see what power the valve is getting, if that isnt clear, the temperature clamps would be out to see where the water is flowing.

Well, the pumps an easy check without taking a screwdriver to it, just listen or put your hand to it. If it’s got a variable speed try turning that up too.

It’ll be obvious whether the valve is moving correctly by the temperature of the outflow pipes, no temperature clamps needed IME. Diagnosing why an actuator isn’t operating the valve could well be one for the meter but (no judgement intended!) seems like it would be beyond the OP’s diagnostic ability.

I don’t really like parts darts but based on personal experience my inclination would be to take a punt on swapping out the motor or the whole actuator, it’s easy to do and a relatively small outlay against the cost, time and inconvenience of getting in a plumber or heating engineer. I do understand that may end up being necessary though!

By the way OP, just on case you hadn’t figured it out, the little tab with W M H is just an indicator, the manual override is on the end opposite the screw. They can still be a bugger to move if the actuator has failed but the system is powered up and the motor’s working against you.

If anyone’s wondering… heating back working again 🙂 (Actually too warm in the house currently!)

Heating engineer came out, soon as I told him about the dormant rad and he saw the micro-bore pipework, he knew it was a blockage. Came back yesterday, poured unblocking chemicals into the water tank. Within the hour they’d done their stuff and the downstairs rads started warming up. Most pleased cos the lack of circulation was confusing the heck out of the old boiler. Getting him to quote for a replacement system in the new year 🙂

A good result, luckily you ignored my recommendation to change the actuator. In my defence, I’ve got a system with microbore piping which hasn’t had a blockage in the 27 years I’ve been here. I’ve always run it with inhibitor and renewed it every few years so that probably helps.

I have had to replace the 3-way valve once and the actuator twice though!

I’ve always run it with inhibitor and renewed it every few years so that probably helps.

This with microbore. I flush and inhibit most years – £7.99 for peace of mind.