Halstead Finest Gold Combi - no heating or hot water?

[will_uk]

Hi guys,

I have a a Halstead Finest Gold Combi boiler - around 10 years old. It's mounted in the loft on an outside wall.

Once in a blue moon (perhaps once or twice a year) it has been a bit sluggish when responding to demand for hot water, usually in cold weather. Usually after closing and re opening a HW tap all is fine. Never stopped working and I've never noticed any CH issues. Otherwise it's been reliable and working fine for the 5 or so years I've been with it.

It's now giving a fault. Over the last few days it's been regularly failing to respond to demand for hot water and now it also seems to stop the CH also when this is happening. It tries to start up when it sees demand for either CH or DHW, but then stops 1-2 seconds later. It wasn't bringing up the red fault light/safety interlock - was as if it started up and then decided it didn't need to be operating? Starts up a few seconds later and shuts down after 1-2 seconds again, carries on like this for several minutes.

I had a quick look a couple of days ago - the system pressure had dropped to 0.5 bar so I topped it up to 1-1.5 bar and it was all working okay - or so I thought.

Later that evening it failed to respond to hot water demand (although it must have been working earlier as the radiators were still warm!)

Yesterday in the daylight I thought it worth doing a few basic checks.

The pin that operates the micro switch for DHW on the LHS seems to be working fine - moves in/out when HW tap opened.

I have tested both microswitches (DHW and the other flow one) and they seem fine (under 1 ohm) and operate fine.

The two thermistors both read around 11k ohm (seem fine)

I then isolated the water and drained the hot taps. I stripped the diaphragm from the top and then took the larger one out from the RHS - they were both okay (not split etc). I then removed the diverter valve from the RHS which was very dirty and sticking when moved. I had a brand new one (was left with the service manuals from 5+ years back) and a new brass bush/plug so I fitted these instead.

I also had another valve/pin thing for the LHS one (the one that operated the HW microswitch) but as this seemed to be working okay and I didn't have a suitable spanner to remove the nut I had to leave it.

Put it all back together, bled the hot water taps and pressurised it all back up to 1 bar or so and it all seemed to be working fine, hot water on/off fine and the heating working spot on. Used it several times since yesterday afternoon without trouble.

Got up this morning and went to have a shower...cold water! Arghh, heating had been on this morning so confused now.

Looked at the boiler and it's doing the same as before. Tries to start up on demand for HW or CH but it shuts down after 1-2 seconds. Interestingly the red fault light was slowly flashing for the first time. Powered it off and back on again and it started up so I could shower.

Stuck at work now and not sure what's best. I'd really like to be able to fix it myself but if it's not in the water block then obviously I'll leave it to a pro.

Any advice or pearls of wisdom? Is this a common fault?

The only concern I have was the valve I replaced was quite dirty (black and sticking) so does that indicate a grotty state of my CH circuit?

Many thanks and any help much appreciated. Sorry for the lot post but wanted to give as much info as possible!

Will

 

[Agile]

I think you have a pump proving switch.

If so is it apparently correctly operating the microswitch when the pump is powered?

Sounds as if your system water is very dirty.

Tony

 

[will_uk]

There is a second microswitch on the top that Halstead refer to as a 'primary flow switch' - is this it?

The microswitch buzzes out at under 1 ohm and I'm pretty sure it was clicked in place when the boiler was cutting in/out earlier. Unless it's stuck on and needs to be seen 'off' first (?)

One last thing I noticed - could be a red herring - but the system pressure did increase a bit when the heating was running yesterday - from around 1/1.5 bar up to nearly 2 bar? Not sure if this is relevant though?

This is what the old valve looked like. Dirty I think (was sticky when operated). House is a 70s build but all the radiators were new around 5 or so years back.


Thanks for taking the time to reply - much appreciated!

Will

 

[Agile]

Yes, that's the pump proving switch.

Your water is or has been pretty dirty to gunge up the diverter valve parts like that!

Tony

 

[will_uk]

Cheers Tony,

So how is the pump proving switch expected to operate - I take it you'd expect the pin to be down at first then does the boiler look to see it rise and click the switch after how many seconds (?) once the CH or HW demand comes on? Or just for CH?

Any recommendation for the state of the CH water (ie that valve)? It surprised me a bit because I remember bleeding some rads/towel rail a year or so back and the water that came out was clean but then I guess the debris probably falls to the bottom and/or gets stuck in certain places? Could it just be from a few years back before the rads were changed? Should I add something to the system?

Is the system pressure supposed to rise slightly (from 1/1.5bar to ~ 2bar) in use? I'll check if again when I can (it's working at this moment!)

I think if I can narrow the fault down to the operation of this primary flow switch pin/valve (the microswitch buzzes out fine) then maybe I could order up a service kit for the valve block (all new diaphragms and valves/'o' rings etc) and if that cures it consider getting someone to come and flush out the CH circuit?

Many thanks for your help,

Will

 

[will_uk]

Anyone else able to help?

The boiler is still running but has had the occasional hiccup where it's taken a bit longer than usual for HW to startup.

Questions please:

1) Is there any way of knowing what the flashing 'safety lockout' light would have been for - it was just slowly flashing away but was still trying to run? Hasn't reappeared though.

2) What's the normal expected operation of the top primary flow/pump proving switch? Is it expected to be seen 'OFF' with the pin down and then move to 'ON' with the pin up and operating the switch after what condition? CH or HW demand or both? Does it have a time frame in which it needs to see this switch operate?

3) Any advice re servicing/cleaning the system? The diverter valve was quite dirty/sticky. If I can understand the function of the block/valves/switches better I'll order up all new seals/diaphragms and valves/seals which will hopefully have it running smoothly again - but would be nice to know it's not going to get gummed up again too quickly!

4) Lastly, does the system pressure sound okay? Would you expect it to rise by ~ 0.5 bar with the CH on?

Many thanks again and would appreciate any advice

Cheers,

Will

 

[Gasguru]

Can't be a**ed to read the previous...

The pin should rise with a DHW or HTG demand. The switch "tells" the boiler that there is sufficient differential pressure across the heat exchanger (and therefore water) to commence ignition etc.

The normal reason for the pin not to rise or be weak is a worn pump or partial blockage in the system.

Whenever the boiler is turned on from the mains or a DHW or HTG demand is made the boiler will check the switch and if not made within a specific time the LED will come on AFAIR.

For a normal property the cold pressure should be around 1 bar rising no more than another bar when the rads are up to temp.

 

[will_uk]

Okay, so it sounds like the pressure is normal

Thanks for explaining the operation of the flow switch.

I think it's worth ordering up the rest of the servicable parts for the brass water block - diaphragms, valves and seals etc.

Any feedback regarding system cleaning or flushing would be appreciated - should I drain and refill the circuit adding inhibitor or would that be a waste of time now?

Thanks

Will

 

[Gasguru]

Draining a system alone won't make a lot of difference.

You could add cleaner, run the system and drain.

Refil with inhibitor.

Even on a brand new, cleaned system diverter parts will start to stick after 10 years or so. No amount of powerflushing/chemicals will get the system spotless.