Central Heating Issues!

[Ripperoo]

Been having issues with our central heating system, so time to get it sorted and hope the useful folk on here can offer some advice/insight.

The boiler broke down at the end of May 2018 (the pilot light would not stay lit).

Our usual plumber/HE figured it could be one of a few things, so opted for the cheapest fix first and changed the thermocouple, but still the issue persisted.

He ended up replacing the gas valve (Honeywell) and got the system up and running and hot water was restored, but stupidly, I forgot to check the heating (it was the beginning of the hottest June ever after all)!

So, it was only recently we noticed the central heating side of the system would not kick properly via thermostat/programmer.

The only way to get the heating to work was to use the old flick the silver lever on the motorised valve.

The heating does work and when it goes off the lever slowly returns to the resting position.

I've read so many articles that my head hurts, so have come here.

What could be the issue?

I initially thought our plumber/HE had wired something incorrectly, but he's been doing this for years and I don't want to insult him by getting him to check.

I'm leaning towards the motorised valve, but have also read similar situations where it has been down to the programmer.

The entire valve/actuator was changed a few years ago by the same plumber/HE), but if I do need a new one, which one do I need look for?

I've seen similar looking Danfoss actuators advertised as zone valve, 3-port diverter, 2-port, 3-port with mid-point.

Ahhh, my head is battered!

The current one is a Danfoss HSA3 with four wires (grey, orange, white/brown and blue).

Was the correct type used when replaced a few years ago?

Also the old Danfoss SET3 dual channel mechanical timer was changed to a Danfoss DP975, which IIRC was a direct swap.

I've since learned that there are "dip-switches" on the rear, so could these have been set wrongly and still let the system work in a fashion?

How should they be set?

I do have another programmer (Danfoss FP715), but I think the terminations are different, so not a direct swap.

I also wonder what my CH system would be classed as (apart from being ancient)? Gravity HW with pumped CH perhaps?

Yesterday, I drained the system at the lowest radiator drain-off and manually removed a lot of sludge from the tank using a vacuum pump (there was quite a lot)

I've now refilled the system with fresh water, adding a litre of Sentinel X400 in order to run it for a to run for a day or two.

Bled all radiators before switching on the heating and there was a bit of gurgling, knocking and banging coming from the airing cupboard initially, which I guess was air locks at the pump.

All these noises have now stopped and everything is now pretty quiet.

I will be draining/flushing the system again in a day or two and refilling with fresh water, adding a litre of Sentinel X100.

I understand our central heating system is quite old (installed approx 20 years ago), but when we've looked into having it changed, several CH guys have said only change it when it dies and parts cannot be found anymore as despite being inefficient, it would take many years to recoup any of the outlay of a new system.

Would that be the general consensus?

The system comprises:

Lounge
Baxi Bermuda (45?) Boiler
Danfoss FP975 Programmer
Radiator x 1 (TRV)
Fused Spur

Hallway
Sunvic TLX Room Stat
Radiator x 1 (No TRV)

Airing Cupboard
Cylinder (With Immersion Heater)
Grundfoss Selectric Pump
Danfoss AT Cylinder Stat
Danfoss HSA3 22mm 4 Wire Motorised Valve
Danfoss Wiring Centre

Loft
Hot Water Supply Tank (Large)
Central Heating System Supply Tank (Small)

Rear Hall
Radiator (TRV)

Bedroom 1
Radiator (TRV)

Bedroom 2
Radiator (TRV)

Bedroom 3
Radiator (TRV)

Bathroom
Towel Rail (TRV)


Sorry for the long post!

 

[terryplumb]

So ,after reading the potted history ,volume one ,of your central heating ,it seems that your problem is the central heating will not come on when you want ,but the domestic hot water does. My guess is the motorised valve but there is no substitute for an on site diagnosis by a good c/ heating engineer.
Without going into a long winded post ,the timer /programmer ,thermostat,and motorised valve are all suspect and your guy on site ,with a multimeter should make light work of diagnosing the problem. Regards Terry

 

[Ripperoo]

My guess is the motorised valve but there is no substitute for an on site diagnosis by a good c/ heating engineer.

Thanks Terry.

Well, I've ordered a new motorised valve as we've had one fail in the past and from what I read, some don't last more than about 5 years.

Whilst looking around, I came across NEST systems, but unsure whether they work with my kind of CH system.

Any ideas?

 

[terryplumb]

Nest ....hmmm more things to go wrong !!
Buying parts without diagnosing what exactly is at fault ,aint particularly wise.

 

[Mottie]

It’s done quite often in the motor trade. I call it playing 'parts darts' where some garages just start chucking parts at cars in the hope it gets a result!

 

[Ripperoo]

Buying parts without diagnosing what exactly is at fault ,aint particularly wise.

Assuming NEST would work, I wouldn't be buying it until I get the central heating back to fully working condition.

Just need an answer as to whether the NEST system would work with my CH system (when fully functional).

 

[terryplumb]

Assuming NEST would work, I wouldn't be buying it until I get the central heating back to fully working condition.

Just need an answer as to whether the NEST system would work with my CH system (when fully functional).

I was referring to buying motorised valve before establishing if its at fault ,not nest. What do you hope to gain from having " nest" fitted ? Which in all probability can be fitted to your " ancient" system .

 

[Ripperoo]

I was referring to buying motorised valve before establishing if its at fault

If it's not the MV, it's not a great problem as it will do as a spare (it will go eventually if hasn't already).

 

[Ripperoo]

FAO Terryplumb, that wasn't a sarcastic "Thanks", was it?

Just so you know, I wasn't being ungrateful with my "Anyone?" comment (which is now gone).

That comment was a follow up to a comment I made myself regarding the changing of a thermostat and was an attempt to get a response after there had been no replies.

I subsequently ended up editing the comment and starting a new thread.

So if you thought I didn't value your comments, rest assured, that is not the case.

 

[Ripperoo]

My guess is the motorised valve

Well, I was leaning towards the MV as mentioned in my first post and with your educated 'guess', that was enough for me to take a chance and order one and it turns out that was what it was.

Once the MV was fitted and working correctly, I also replaced the room stat and tank stat (going to also replace the programmer) with the valuable info from yourself and other forum members.

I cannot thank you all enough.