Glowworm Ultimate 50FF - Now only lights if Heating & Hot Water requested

[chrish2]

We have a Glowworm Ultimate 50FF that was installed since the house was built (2000). Since the first boiler breakdown the boiler seems to have been a bit of enigma for engineers to correctly diagnose and fix faults.

Now years late it seems to have developed a habit of both struggling to light and only lighting if both heating and hot water is requested. Given we don't use the heating unless manually requested we didn't really notice until the weather started to get colder. Short term fix was to turn both on and hope it would eventually light.

Long term fix is our Home Emergency Cover from our house insurers. We are now on our 4th visit by 3 different engineers over 2 separate call outs! Everything is covered but starting to be disappointed that the parts and time been spent on it hasn't got to be fully in order.

After today's visit the boiler seems to have no issue lighting in response to request for hot water (as soon as requested). However with that so much improved the fact it never even bothers to do anything if heating is requested on its own is now much more obvious.

My understanding is some systems (gravity feed) can only have heating when the hot water is on. We have been able to use our programmer for two decades to request heat or hot water independently.

I have just checked the following combinations
----
Boiler does not attempt to start if;
* Heating requested, hall thermostat high
* Heating requested, hall thermostat high, hot water requested, cylinder temp low

Boiler starts immediately if;
* Hot water requested, cylinder temp high
* Heating requested, hall thermostat high, hot water requested, cylinder temp high
----

Kit involved
* Boiler = Glowworm Ultimate 50FF
* Programmer = ChannelPlus XL Model H21
* Pump† = GRUNDFOS UPS3 15-50/65 130
* Mid Position Actuator = Code GBMVSP-23
* Thermostat = Siemens Landis & Staefa (unknown model)

Annoyingly they don't give you paperwork any more telling you what was done and over 4 visits it's hard to keep track of everything.

† This is not the original pump as during these recent visits it had to be replaced (started to make an awful noise)

Based on the setup is there anything trivial or a common fault that might be causing this? My uneducated guess is something been incorrectly re-commissioned during one of the visits on the controls side. Hopefully if I hint strong enough the next visit might be the 5th and final!

 

[ianmcd]

My understanding is some systems (gravity feed) can only have heating when the hot water is on

Common mistake you are mixing up gravity HW with a fully pumped Y plan system, you have an open vent system , not a gravity system, post some pics of all controls and pics of your HW cylinder

 

[chrish2]

Attached is most of the heating system except the tank in the loft.

 

[ianmcd]

OK you definately have an open vented, Y Plan fully pumped sytem, not a gravity HW system, when you select CH on only and not HW on doest the HW on indicator come on without being selected ?

 

[chrish2]

Sorry, the programmer picture didn't attached to my last message.

On the programmer I can turn on Hot Water or Central Heating and only one light shows for the relevant service. There are 4 possible combinations as pictured this time

 

[terryplumb]

Basic checks at the wiring centre would reveal what the issue is.

 

[chrish2]

I've just checked that the actuator cycles through the 3 phases. Each combination of the HW, CH as well as HWCH from the controls results in the actuator indicator been in a new location. It is missing the label with the text next to the indicator so can't confirm 100% they are been set to the right value each time but they are been set to "something" different for each combination.

Something to note, when the pump was replaced there was an escape of hot water (isolator valves around the pump has seized), I suspect the hot water may have washed off the label on the side.

Based on all this would is it likely the cause of the issue to be the wiring in the wiring centre been incorrect or something failing with the the mid-position valve (either mechanically or electrically)?

 

[ianmcd]

then you programmer is set as fully pumped, has it ever worked properly , if yes I would be looking at a fault actuator, if no I would be looking at the wiring

 

[terryplumb]

Mid position valve problem most likely. The MPV sends voltage to the boiler for it to fire up. Checking the voltages at the wiring centre would confirm if the MPV is ,or isn't doing so.

 

[chrish2]

Programmer has previously worked correctly.

Seems we have our likely suspect (MPV), if we was in sub zero temperatures I would dig out a multi-meter to confirm further but just having a good idea what the likely fault is caused by make me feel that this all can be resolved on a 5th visit! Glad it's covered on the policy otherwise I would be livid at this stage.

Thank you both, I have a much better understanding of how this all works now.

 

[chrish2]

Update on the case for anyone looking in the future. Wiring check confirmed MPV was not outputting the voltage to fire the boiler (heard something re 50v instead of 240v). MPV "outter" part replaced (with Drayton MA1) and we are able to request heating only. Feel all set for winter now