Curious heating behaviour? (boiler does not fire up on demand)

[Tanel]

OK, so I recognise that there have been posts on similar issues so apologies in advance if we're going over old ground. I simply cannot get my head around the way my heating is behaving.

Quick description of the setup:-

Boiler is downstairs, a "Glowworm Ultimate" - old. Installed 80s/90s I think. Yes, an easy reply would be "get a new one" but insofar as we're talking about it working mechanically, it works, and was recently serviced. It comes on, I do get hot water and my radiators do heat up, when they want to (see below).

Hot Water Tank on the first floor. Has its own white thermostat on the side but I don't usually touch this. There is also an electrical immersion heater in it with a switch but again, I don't usually have that on as my HW requirement is quite low.

Controller is a Lifestyle LP522 - again, not too new. Found it quite fiddly in relation to timing etc so for now, and to hopefully eliminate some possibilities in relation to the problem, I have left this at "ON" both for CH and for HW.

Thermostat is a wired Drayton 30002 in the living room. This was installed professionally about 6 months ago, new. I've checked how this has this been wired, Red in COM, Black in ON, which I understand to be correct. Display is fine, batteries checked.

There is a motorised valve (white box) with "WMH" on it connected to the boiler. This seems to be working, I can hear the motor and see the valve position moving from time to time.

The problem -
1. House gets cold.
2. I turn the thermostat up and it clicks, and it calls for heat (the flame symbol comes on). However, the boiler does not fire up at that point.
3. Radiators do not warm up, despite thermostat calling for heat.
4. Several hours later, when I am not expecting it, the boiler may fire up.
5. Again, when I am not expecting it, and possibly several hours later, my radiators will heat up, when I don't necessarily need them to.

In my last house I had a combi boiler and when the thermostat clicked on, as I recall the boiler would fire up straight away. Within 10-15 minutes the radiators would warm up. That's basically what I expected to happen here.

Now since I have a HW tank, what I understand should happen is that when there is a call for heat, hot water is immediately or at least fairly quickly pushed around the radiators to warm the house up. If there is not enough water in the radiators at a hot enough temperature, the boiler fires up to heat more. Maybe I've got that wrong.

This would explain the boiler not firing up immediately if there is already enough hot water in the system, but to me it does not explain why my radiators are not heating up once the thermostat calls for heat. If it's not the room thermostat determining when hot water is pumped around the radiators, what else is it?

As for the boiler firing up when there is no call for heat from the thermostat, that's probably less of an issue, except for the fact of me maybe using up gas when I might not need it.

Sorry for the long post, I thought the detail would help, any thoughts/advice would be appreciated. It might be easy enough to just get a new boiler and a new controller, but I'd like to eliminate everything else if possible otherwise I may end up with the same issue again anyway.

Thanks in advance.

 

[JohnD]

is the cylinder circuit gravity flow? there is a setting on the back of the programmer, if it is not fully pumped.

has it always worked like this, or did it go wrong?

please show photos of the motorised valve and the pump, and the pipes around and between them, and of the thermostat on the cylinder. It is possible that, if you experimentally turn up the cylinder stat, the boiler will fire.

 

[Tanel]

Hi John,

Thanks for your reply.

I moved in in February and it was a little erratic then too. As the weather warmed up through the spring and summer it became less noticeable as an issue, because of course I didn't really need to heat the house as much. Now that the weather has turned colder again, I'm noticing it more.

This is the view of the boiler and associated components:-

A couple of close ups on the valve section:-

This is a close up of the controller section:-

And this is the thermostat on the HW cylinder:-

I am not sure about the "gravity flow" point, but if it helps, the boiler is on the ground floor, the cylinder on the first floor, and there is also a water tank in the loft.

Kind regards.

 

[jackthom]

Are you getting plenty of hot water in the cylinder so the problem is purely with central heating?

One possibility is that the only time your heating is working is when the hot water cylinder is also asking for the boiler to fire up.

If this is the case it would often indicate a problem with the 3 port valve, which in addition to directing the flow of water also has the job of switching on the boiler when it motors right across to the H position for central heating only.

 

[CBW]

I would say an issue with the 3 port mid position valve (the one with WMH on it). I suspect it’s not energising fully for heating and only coming on with the hot water demand, or eventually making the end switch. You appear to have currently or have had a leak with all that green showing at the tee.

 

[Tanel]

Hello Jack.

My hot water requirements aren't high as I live alone, so I haven't noticed a lack of hot water per se. I know that sometimes I have to run the tap a little before the water heats up (maybe 15-20 seconds) and at the other end of the scale, the water can start to cool after a particularly long hot shower, but I haven't experienced this as a particular problem.

It's the central heating, really. My thermostat is up at 22 right now, the programmer is set to on, but the radiators are off and there is no sign of the boiler starting up or any water moving around the system and filling them.

 

[JohnD]

OK, you have a 3-port valve, and it is fully pumped, so if it is wired correctly, it should work.

Have you tried turning up the cylinder stat yet?

I can't remember what are the effects of having the rear switch set to "gravity" on a fully pumped system (I did once convert one myself) but doubtless one of the heating engineers will know if this is relevant or a red herring. I ask because, on a gravity system, you can only have heating while the HW is on, which might be happening in your case.

Very annoyingly, your programmer appears to have the boiler installed in front of it so the programmer cannot be hinged up or taken off.

 

[vulcancontinental]

Turn the room stat to max, does the heating come on? NO? Get someone in.

 

[jackthom]

Next time the boiler fires up try to check if it is also heating the radiators at the same time, ie the valve in the M position.

I suspect it only fires up when in the W or M positions and not the H position.

W is water only, H is heating only and M is the mid position for both together.

 

[Tanel]

Have you tried turning up the cylinder stat yet?

Going to try this now - I'll put it up to 60. I am reluctant to whack it up too much in case the water becomes too hot to touch.

Very annoyingly, your programmer appears to have the boiler installed in front of it so the programmer cannot be hinged up or taken off.

Yes. Going forwards I will probably have to get that repositioned.

Thanks.

 

[Tanel]

Next time the boiler fires up try to check if it is also heating the radiators at the same time, ie the valve in the M position.

I suspect it only fires up when in the W or M positions and not the H position.

W is water only, H is heating only and M is the mid position for both together.

Thanks Jack.

I'll watch out for that and report back.

 

[Tanel]

I would say an issue with the 3 port mid position valve (the one with WMH on it). I suspect it’s not energising fully for heating and only coming on with the hot water demand, or eventually making the end switch. You appear to have currently or have had a leak with all that green showing at the tee.

Thanks Chris.

I think the "green" is historic and there isn't any current evidence of a leak. If it's a purely cosmetic thing I can live with it, but of course if it's interfering with operation then that's something to consider further.

In terms of the valve "energising" for heating, are you basically saying that a call for heat from the thermostat should divert that valve over to H (if no HW is being used at that moment) or to M (if HW is being used at that moment)?

I just ran the hot tap for about 30 seconds, water was hot, the boiler did come on. The valve stayed over to the right, in the H position, where it was before. Radiators are making tiny noises but too soon to tell if they are warming up properly.

UPDATE - 5 minutes have passed boiler still on, WMH valve still at H, and radiators gently warming up. (I haven't tweaked the cylinder thermostat yet).

 

[CBW]

In terms of the valve "energising" for heating, are you basically saying that a call for heat from the thermostat should divert that valve over to H (if no HW is being used at that moment) or to M (if HW is being used at that moment)?

Yes, this is how it should work. Try selecting hot water only and see if the valve position changes to W. Then see if the radiators come on. If they do let me know. If it just moves and there’s no heat, then try heating only.

 

[Tanel]

Yes, this is how it should work. Try selecting hot water only and see if the valve position changes to W. Then see if the radiators come on. If they do let me know. If it just moves and there’s no heat, then try heating only.

I turned down the thermostat and the valve moved over to W. I turned it back up, and the valve moved to M. I tried this several times with consistent results. That suggests to me (as a layman) that the valve is ok.

The radiators have warmed up but it seems the boiler/radiators only came on because the HW ran for a bit, rather than coming on only because the heating thermostat was triggered. Does that make sense? I would have thought that HW and CH are totally independent of each other but apparently that's not happening with my setup. Is that normal at all?

Running the hot tap when I want to get the boiler/radiators to come on would be a "workaround" but it doesn't seem to be a proper solution!

 

[jackthom]

Disable hot water at the programmer and then try increasing the room thermostat temperature to double check that the boiler is still not coming on for heating-only, ie valve at H position.

When at H position give the lever some help to go as far as possible in that direction, just in case it's a bit sticky and not going far enough. It needs to go far enough to operate the internal microswitch which turns on the boiler.