Advice on Glow Worm boiler please

[daWilko]

Hi All,
I'm new here but fairly active in Sparks Forum (@Last Plumber where are you?). I've recently moved and have a Glow Worm Flexicom 18hx. Heating is gravity fed, y plan, external pump, small loft tank for CH and large tank to feed taps and HW. It all works, but not very warm. The boiler seems to run a bit strangely and hence my post here.
I'm used to setting a temp on the boiler, demand from room stat, pump on, burner on, achieve temp, run till demand satisfied or timer off. What I get with this GW is - runs up to set temp (say 80C), burner off, pump still running so temp cycles down to say 40C then burner ignites and we go back to 80C and repeat. So I'm really only getting 60C on average, if that makes any sense. Does that sound normal for this model? Many Thanks !

 

[ShaunCorbs]

how old is the pump ?

sounds like it cant get rid of the heat fast enough

 

[daWilko]

how old is the pump ?

sounds like it cant get rid of the heat fast enough

Hi Shaun, thanks for your thoughts. The pump is 3 speed Grundfos, set on 3. Its the original pump from installation by the looks, which was June 2010 (last fella kindly left me the logbook). Pump does have water in it, a slow drip with the screw out. I've turned off half the rads to try to get warmer, but this maybe been the wrong thing . The rad water is yuck.

 

[Gasmk1]

with the screw out when pump running use a small screwdriver to try to stop the pump spinning there is a small indent that makes this possible if you can syop the pump easily then the pump is goosed. and needs changing

 

[jtsplumbing]

Could be a Pump fault did you get the system checked ? most people don't, get your boiler checked could have some issues.

 

[Last Plumber]

Hi All,
I'm new here but fairly active in Sparks Forum (@Last Plumber where are you?). I've recently moved and have a Glow Worm Flexicom 18hx. Heating is gravity fed, y plan, external pump, small loft tank for CH and large tank to feed taps and HW. It all works, but not very warm. The boiler seems to run a bit strangely and hence my post here.
I'm used to setting a temp on the boiler, demand from room stat, pump on, burner on, achieve temp, run till demand satisfied or timer off. What I get with this GW is - runs up to set temp (say 80C), burner off, pump still running so temp cycles down to say 40C then burner ignites and we go back to 80C and repeat. So I'm really only getting 60C on average, if that makes any sense. Does that sound normal for this model? Many Thanks !

Hello there, I'm here!
It does sound like a lack of flow or slow flow as above.
Have you checked all the rad valves are open?
Do you know what the flow and return temperatures are? That will help a lot!
Do all the rads get hot when it's up to 80 deg?
Do you know if there is a bypass?

 

[jtsplumbing]

Take it the boiler is set to max temp ? Do you have a Room stat ? but if its something you want to try B4 calling someone out Replace the Pump first. maybe photo of controls would help.

 

[daWilko]

Hi Guys !
Had a look in at lunch time and here's the update :
With pump running I bravely stuck my insulated PZ1 into that dent. I could slow the pump but it gave a pretty good fight. Definitely not wimpy. So pump itself probably ok (?).
The boiler has had 8 services, last one 15/9/17 (eng id supplied and all). Amazing really, considering the state of the loft tanks, but that's another story.
It does sound like the flow from the pump has been an issue as I've opened all rad valves now and its heating better/for longer now. And the rads that do feel hotter now.
Despite all the services on the boiler, the state of the rad water makes me think they've run it for some years without inhibitor. So it might have lumps of muck circulating (?).
For want of knowledge, I've set flow at 75C on boiler, but don't have figure for return. There is no bypass fitted, but it seems a requirement in the installation manual (just readin up ). I guess Installer thought the nearby bathroom towel rad would do (?). There is a new Honeywell 3 wire stat in the Lounge. Old one was original Honeywell fitted donkeys yrs ago and plastic was smacked about. New one is the updated version, a T6360B ...

I'll report back on performance tomorrow. Thoughts and ideas most welcome !

 

[jtsplumbing]

Hi Guys !
Had a look in at lunch time and here's the update :
With pump running I bravely stuck my insulated PZ1 into that dent. I could slow the pump but it gave a pretty good fight. Definitely not wimpy. So pump itself probably ok (?).
The boiler has had 8 services, last one 15/9/17 (eng id supplied and all). Amazing really, considering the state of the loft tanks, but that's another story.
It does sound like the flow from the pump has been an issue as I've opened all rad valves now and its heating better/for longer now. And the rads that do feel hotter now.
Despite all the services on the boiler, the state of the rad water makes me think they've run it for some years without inhibitor. So it might have lumps of muck circulating (?).
For want of knowledge, I've set flow at 75C on boiler, but don't have figure for return. There is no bypass fitted, but it seems a requirement in the installation manual (just readin up ). I guess Installer thought the nearby bathroom towel rad would do (?). There is a new Honeywell 3 wire stat in the Lounge. Old one was original Honeywell fitted donkeys yrs ago and plastic was smacked about. New one is the updated version, a T6360B .
View attachment 32739I'll report back on performance tomorrow. Thoughts and ideas most welcome !

Be a good idea to put some system cleaner in I use Fernox heavy duty cleaner F5 just follow instructions on bottle

 

[ShaunCorbs]

Agree with the above stick some x800 in for a week and then re drain it

 

[gmartine]

Stat in lounge? Is it a case of lounge getting up to temp and other rooms aren't?

 

[Last Plumber]

Hi Guys !
Had a look in at lunch time and here's the update :
With pump running I bravely stuck my insulated PZ1 into that dent. I could slow the pump but it gave a pretty good fight. Definitely not wimpy. So pump itself probably ok (?).
The boiler has had 8 services, last one 15/9/17 (eng id supplied and all). Amazing really, considering the state of the loft tanks, but that's another story.
It does sound like the flow from the pump has been an issue as I've opened all rad valves now and its heating better/for longer now. And the rads that do feel hotter now.
Despite all the services on the boiler, the state of the rad water makes me think they've run it for some years without inhibitor. So it might have lumps of muck circulating (?).
For want of knowledge, I've set flow at 75C on boiler, but don't have figure for return. There is no bypass fitted, but it seems a requirement in the installation manual (just readin up ). I guess Installer thought the nearby bathroom towel rad would do (?). There is a new Honeywell 3 wire stat in the Lounge. Old one was original Honeywell fitted donkeys yrs ago and plastic was smacked about. New one is the updated version, a T6360B .
View attachment 32739I'll report back on performance tomorrow. Thoughts and ideas most welcome !

Out of curiosity, try it from cold with the 'towel rail by-pass' shut and all the rads open, see how it behaves then. Don't leave it with the towel rail shut off if that is the only by-pass.

 

[daWilko]

Stat in lounge? Is it a case of lounge getting up to temp and other rooms aren't?

Hi - good thought - that's why the replacement stat I put in has the handy demand lamp in it so I can keep my eye on it .
The boiler cycling still occurs when demand is constantly applied.

 

[daWilko]

Update - I drained a few litres of the muckiest water last night. Now withall rads open, timer on, CH demand constantly on - the boiler fires and heats normally bringing the system up towards max temp setting. Boiler seems to go 2 deg past this and turns burner off. Then waits a period and starts the process again. It's taking say 20 min to bring system up to 75+2 now (a good thing really) and heat from rads is ok.
I will get system cleaner today and go from there. Thanks for your help

 

[Last Plumber]

Update - I drained a few litres of the muckiest water last night. Now withall rads open, timer on, CH demand constantly on - the boiler fires and heats normally bringing the system up towards max temp setting. Boiler seems to go 2 deg past this and turns burner off. Then waits a period and starts the process again. It's taking say 20 min to bring system up to 75+2 now (a good thing really) and heat from rads is ok.
I will get system cleaner today and go from there. Thanks for your help

I would recommend F3, leave it in a couple of weeks then get it hot and drain it all out, re-fill and dose it with F1 (both Fernox).
Then fit an Auto bypass in the right spot and balance the system.
You really want your return below 53 degrees!

 

[gmartine]

Hi - good thought - that's why the replacement stat I put in has the handy demand lamp in it so I can keep my eye on it .
The boiler cycling still occurs when demand is constantly applied.

As it's a regular boiler my concern would be if the stat is in lounge (with TRV) they'd be no interlock.

 

[jtsplumbing]

I would recommend F3, leave it in a couple of weeks then get it hot and drain it all out, re-fill and dose it with F1 (both Fernox).
Then fit an Auto bypass in the right spot and balance the system.
You really want your return below 53 degrees!

If system is this dirty F3 wont be strong enough F5 would be better bet, I only use F3 to flush out new systems. But each to his own.

 

[daWilko]

Hi All - Put X800 in over the weekend, drained, refilled, drained, refilled, added X100. The boiler is now running much longer and heats effectively. Many Thanks ! Mind you, it's good the carpets are being replaced, as all the drain off point washers were shot to sh ... non functional.