"Systemate 2000 " Intermittent Space Heating / CH Circulation & Boiler Overheat

I have recently been called out to a system mate 2000 coupled to a Glowworm 12hxi heat only boiler displaying f5 overheat fault.

The Gloworm fault finding table points towards no pump over run , however i believe the ACB on the SM2000 activates a 3 min pump over run when the heat in the thermal store is satisfied (77deg c) and the boiler shuts down ?

Sw2 store reading +60degs c, the ch circulating pump activates and the radiators warm.
I don't get any error codes when pressing sw1/2
SW1 readings are 74lower -77upper ( degc ) is this correct?.

I reset the F5 fault on the Gworm flow stat by heat exchanger and switched back on, the boiler fired immediately to start heating the store i assume.( GW output set to high.) I then initialised the start up sequence on the sm2000 by switching on/off. The LED initialisation sequence all seemed ok. After the store reached temp (60deg) i called for 25deg on the room stat & the ch circulating pump started.The radiators heated to my delight, however within 1/2 an hour the ch pump was very hot to the touch but the rads cooled. After listening to what sounded like the ch pump struggling / stopping / starting I replaced the 15/50 Grunfos pump recharged to 1 bar added inhibitor & bled the system. I started up the system bled some air from the GW heat exchanger as no AAV's were fitted and the boiler is above the SM2000. All seemed brilliant Once the store was back to temp the radiators warmed brilliantly and all was well.

The next day i was re contacted by the customer with a F5 again......!!!

I noticed that the towel rail circuit is always piping hot, but the return is not plumbed into the 15mm pipe as shown in the SM2000 installers instructions and must return another way. (no visible pipe-work) Could this cause complications....Tried testing for the fault with the towel rad / bathroom rad trv's off to see if any different but not alot different..

HELP..................................?

Hi Dave,

I've had a fault similar to this. IIRC an intermittent fault on the control board was sometimes feeding a rapidly changing variety of voltages to the room stat, which in turn (indirectly) powers the pump. During the periods of unstable voltage the pump would either spin very slowly or stop and oscillate instead of spinning. When it did this it emitted a weird growling noise.

Like you I changed the pump and got a call-back the next day.

I think I fixed it in the end by connecting a live supply directly to the room stat from the timer output, bypassing the 'official' control board room stat supply.

Cheers, Mike

Is the Glowworm 12HXi related to the 18HXi? We had an overheat fault (flashing F9 I think) which the first bod out to "fixed" by replacing the thermistors and overheat thermostat. Which was OK for about a week and then went again. The next guy out thought pump but then said "Has anyone ever replaced the burner door seal on this?" No, why? "Ah because there's a known issue with these, I'll just get the kit from the van".

Sure enough the original seal is rubber and perished, so some hot gas was escaping and then tripping the overheat. The replacement is graphite and there are new nylox nuts to secure the door in the kit.

Yes I believe the 12HXi is identical to the 18HXi except in output. And yes there is not so much a 'known issue' as a straighforward instruction in the Manufacturers Instructions book to replace the burner door seal whenever it is disturbed. The original neoprene seal shrinks with age and cannot be re-used safely. The new graphite one does not exhibit this 'feature' ;-)

I'll be surprised however if this is the reason for your overheat thermostat tripping. I predict the problem will return. Overheat tripping is certainly a 'known issue' with the HXi and is associated with restricted or low water flow through the heat exchanger, which is most likely to be corrosion deposits clogging the heat exchanger. I take it yours is fitted to a Sytemate 2k as you're posting in this discussion?

The boiler pump on the SM2k is adjustable. What speed is yours set to? Try turning it up to speed III if lower. If it is already on III it is likely to be corrosion deposits, although another possible cause would be thermostatic rad valves. These NEED a bypass to be fitted to prevent low boiler flow rates as the house warms up. Often a rad is configured by the installer as a bypass (the one in the same room as the room stat) but if the user turns that rad OFF (or down), this will cause nuisance overheat tripping of the boiler - as will the complete absence of a bypass circuit when TRVs are fitted.

Cheers, Mike