CH weirdness - hot water ok, rads not so much. Airlock?

[Steamrunner]

Hi all,

I've been trying to work out what's going on with my heating system - lots of rapid learning, but there's no substitute for asking people who know what they're talking about...

Just bought my mum's house, haven't lived there since the 90s but roughly know the history of the CH system. Has been fine for donkeys years, apart from a new pump about ten years ago (system itself is around 20-25 years old). It's an open system, F/E tank in the loft, gas powered boiler (Ideal Concord HRS) with Honeywell 3-port motorised valve next to the hot water tank.

Recently the rads have been slow to heat up, and not consistent in their heating - different ones heat up at different times. They've all got their inlet valves open, haven't touched their outlets 'cos I don't want to affect the balancing (assuming it is balanced properly!). Anyway, my first thought is there's air in the system, so I've tried bleeding the radiators and some produce water right away, whereas others either have air hissing out followed by nothing (no water, no hissing), or just the nothing (no hissing at all). There's also plenty of noise from the pipes/boiler/pump which seems to be consistent with air in the system.

I've checked the F/E tank (it's an open system) and that has water in it to above the outlet, and the ballcock valve works perfectly - so there is water available, but it's not going in to the system.

The pump is working (it's moving when you open the bleed valve cover) so my next thought, after some reading, was the motorised valve (a three-port Honeywell 4073A). Having whipped off the cover and switched the heating controls between CH/HW, Off and HW only (there's no CH only option) I couldn't see anything moving and I couldn't feel or hear the motor. However there was a brief "bubbles" sound when the switch was thrown between CH/HW and HW only - but nothing else. Finally, the lever on the head unit moves around real easy - there's no resistance with the boiler on or off. It's almost as if the lever isn't even connected. The hot water tank heats up very nicely regardless the whole time (I mean when the boiler's on), so that's clearly getting what it needs. Since there's no CH only option I can't tell if the CH water is going to the HW system when it shouldn't.

Now, there has been some work recently - two rads removed, one of them replaced with a towel warmer and the other put back in a different location (and the underfloor plumbing modified to accommodate these changes). I imagine this may well have introduced air into the system. However this was after the "nothing coming out of the radiators" symptoms first appeared.

From what I've read, it seems as though water may be prevented from entering the system if the motorised valve is not moving, and since my one has a dimple on the cover this apparently means I can whip off the head unit without getting wet to see if the valve itself works or if that's seized. I'm going to have a look at that tonight, but wanted to see if anyone else had any ideas?

Please let me know if I've left off any useful information and I'll update accordingly!

Cheers!

 

[Softus]

Recently the rads have been slow to heat up, and not consistent in their heating - different ones heat up at different times.

Consistent with a sludged up system. Has inhibitor been added at any time?

Anyway, my first thought is there's air in the system, so I've tried bleeding the radiators and some produce water right away, whereas others either have air hissing out followed by nothing (no water, no hissing), or just the nothing (no hissing at all).

If you bled the system with the pump running that you might have dragged air in.

...there is water available, but it's not going in to the system.

How have you determined that it's not going into the system? For example, if you drain off a cistern of water (in quantity), with the cold supply to the F&E cistern shut off, does the cistern empty? If not then you have a blockage in the cold feed.

The pump is working (it's moving when you open the bleed valve cover)

Spindle turning doesn't mean that the pump is working - it could be worn out.

switched the heating controls between CH/HW, Off and HW only (there's no CH only option) I couldn't see anything moving and I couldn't feel or hear the motor.

Whether or not the motor moves also depends on the demand from the room and cylinder thermostats, so your experience is inconclusive.

Now, there has been some work recently.... However this was after the "nothing coming out of the radiators" symptoms first appeared.

What was the quality of the water coming out when the system was drained?

From what I've read, it seems as though water may be prevented from entering the system if the motorised valve is not moving,

Not generally with a three port, although it depends how your system has been plumbed as to whether or not air can lodge anywhere.

 

[Steamrunner]

Consistent with a sludged up system. Has inhibitor been added at any time?

Don't know for certain.

If you bled the system with the pump running that you might have dragged air in.

Yes, this is quite possible - I didn't know about only doing it when the pump was off.

How have you determined that it's not going into the system? For example, if you drain off a cistern of water (in quantity), with the cold supply to the F&E cistern shut off, does the cistern empty? If not then you have a blockage in the cold feed.

Good point. I haven't found a drain-off point yet, except for what looks like one near the hot water tank but that's on the 1st floor not the ground floor. I'll try that and see what happens.

Spindle turning doesn't mean that the pump is working - it could be worn out.

True, but I was figuring that if the pump wasn't working, why would the hot water tank still be heating the water for the taps? The immersion heater is switched off but I'm still fine for hot water. So that, plus spindle going, made me think the pump was ok - I appreciate I could well be wrong of course!

Whether or not the motor moves also depends on the demand from the room and cylinder thermostats, so your experience is inconclusive.

I realised that, but since the heating effect of the radiators is now very spotty the room thermostat is clicking at around 15 degrees. The hot water tank thermostat is set to about 70 by the look of it, but I have no idea if it's reporting back correctly. The room thermostat seems (again, I could be wrong) to be OK as turning it to below the click turns off the boiler, and turning it up turns the boiler back on.

What was the quality of the water coming out when the system was drained?

Don't know - wasn't there when the radiators were removed, but I'll try and find out. I don't know if the system was actually drained, though.

Thanks for the quick and helpful reply, by the way - as I didn't know anything about central heating systems before the weekend, this is all very useful!

 

[Softus]

How have you determined that it's not going into the system? For example, if you drain off a cistern of water (in quantity), with the cold supply to the F&E cistern shut off, does the cistern empty? If not then you have a blockage in the cold feed.

Good point. I haven't found a drain-off point yet, except for what looks like one near the hot water tank but that's on the 1st floor not the ground floor. I'll try that and see what happens.

The one near the cylinder is likely to be one to drain the cylinder contents. I advise not touching this, because if it's troublesome to seal (without renewing the washer) then you'll have to drain the cylinder.

Spindle turning doesn't mean that the pump is working - it could be worn out.

True, but I was figuring that if the pump wasn't working, why would the hot water tank still be heating the water for the taps? The immersion heater is switched off but I'm still fine for hot water. So that, plus spindle going, made me think the pump was ok - I appreciate I could well be wrong of course!

It depends on the route of your pipework - it's often possible for the water to circulate to the cylinder by convection (aka gravity). Also, if the pump is worn/weak then it might manage to push water through the coil but not through all the rads.

Whether or not the motor moves also depends on the demand from the room and cylinder thermostats, so your experience is inconclusive.

I realised that, but since the heating effect of the radiators is now very spotty the room thermostat is clicking at around 15 degrees. The hot water tank thermostat is set to about 70 by the look of it, but I have no idea if it's reporting back correctly. The room thermostat seems (again, I could be wrong) to be OK as turning it to below the click turns off the boiler, and turning it up turns the boiler back on.

Unless your three port valve is wired incorrectly then there should be evidence (noise etc.) that it moves when you change the setting on a thermostat.

What was the quality of the water coming out when the system was drained?

Don't know - wasn't there when the radiators were removed, but I'll try and find out. I don't know if the system was actually drained, though.

If you had a radiator moved then it's likely that the system was drained.

Some houses have drain off points outside - take a look around at ankle height on the outside walls...

 

[MANDATE]

Sounds typical of the 3 port motorised valve problem.
If you cant get CH only, then either valve motor or microswitch at fault.
Try HW only and then try HW and CH together. You should hear valve move to mid position. If it functions, it won,t be long before HW is satisfied, then valve may move to CH only but faulty microswitch would prevent boiler from lighting. Or valve may not move and boiler just closes down until HW is demanded again.