Grundfos pump intermittent burning smell?

Calibos

We've a bathroom in an attic conversion installed in 2010. Sink, Toilet and Pumped shower fed by a 1.5bar grundfos Hot&Cold pump in the boiler cupboard which is on the same floor.

Brother reported that over the last few days its taking a long time for the pump to kick in when the shower or taps etc calls for water.

I went up to test last night and the pump came on almost immediately, ie what I'm used to. Flow seemed fine. Left it on for a couple of minutes. I couldn't see or hear anything wrong. Brother was adamant that when he was taking his morning showers before work it wasn't working.

Was told today that this morning in addition to the very delayed flow he could smell a burning smell.

When I am told this later in the day, I go up and run the taps and shower again. Yet again pump kicks in near instant and water flows. Run the shower for 5 minutes. No burning smell. Pump only gets warm to the touch. I get another brother to monitor the shower and pump while I go to the attic. Tank is draining with the shower on and the ball cock valve is allowing refill.

So the pump/shower seems fine any time I try it. Doesn't seem to be an attic tank running dry. Can't be a blockage or filter as water flows all day except the mornings apparently. Could it be something to do with the Mira Thermostatic shower valve. Or the Myson Zone valve for the Hot Water Zone??

Burning smell is a seized pump overheating isn't it. Dust burning? Why is this delayed flow only happening in the early morning and this morning a new symptom of a burning smell....or is my brother imagining the burning smell. ie. Psychosomatic because he knows something is wrong with the pump??

Thoughts?

Calibos

I was awake at 4.45am the next morning. 15 minutes before Hot water was set to come on on the heating system. 5 hours since that bathroom was last used. No problems, pump and flow starts straight away and no smell.

I talk to my brother the next day and he reports that at 8am everything was fine for him too.

Yesterday when last use of that bathroom was midnight and where I didn't do any tests in the wee small hours and first use is again the brother 8 hours since last use at 8am.... 15 second delay before pump and water flow starts after turning the tap on full and again the burning smell from the pump is back.

What is going on??

Could it be some motor bearing or valve seizing after 8 hours of non use but not seizing after 4 hours of non use. lubricant burning or somesuch. Really perplexed by this. On the one hand the burning smell makes me feel like we shouldn't be using that bathroom at the moment and yet on the other hand the bathroom, pump flow seem to run without issue any other time of the day except the morning and seemingly only when that bathroom has not been used for at least 7 or 8 hours.

listermint

If the pump was overheating it should have an automatic thermo sensor that shuts it down. So i doubt it is infact overheating.

What makes you think its the pump at all.

Have you checked everything electrical in the room first. including lightbulbs, phone chargers, downlighters etc.

Calibos

Not sure I'm following your line of enquiry?

First thing in the morning before brother goes to work in the bathroom adjoining his bedroom there is No flow from shower or sink and no pump activation for 15 seconds and sometimes longer with a burning smell quickly forming.

This doesn't happen any other time of the day, certainly any time I've tested. It didn't even happen when the last use was midnight but I tested at 4:30am. The following morning at 8am everything worked fine for the brother too. It seems it's only happening when no one has used that bathroom for 7 or 8 hours.

Airlock forming after 7 or 8 hours?

Calibos

This problem has been infuriatingly intermittent the last week. Which doesn't help diagnosis. Got called by my brother tonight to say that it happened again when the GF went for a shower. No pump activation, low flow then water stopped altogether and smell coming from boiler/pump cupboard. I go upstairs and can smell something in the pump area alright but I wouldn't have said it was a burning smell necessarily. The pump was very hot to the touch.

http://www.amazon.co.uk/Grundfos-AP054-Amazon-Universal-Closed/dp/B00B9I1FNS

This is the pump. A Grundfos STN 1.5B (IRL)

By all accounts a rolls royce of pumps with brass impellers and housings??

So I go to the tap in the adjoining bathroom and pump activates straight away and normal flow of cold water. I turn the mixer tap over to hot and pump activates straight away and normal flow of hot water. Albeit dangerously scaldingly hot water?!?! (Boiler set to 65ºc and Hot water Cylinder Thermostat set to 60ºc)

So I think to myself, well maybe it is time for a plumber alright. However I read online tonight and in previous replies that pump casings can get to 125ºc and its perfectly normal and nothing to worry about. Maybe the smell which actually doesn't necessarily smell like something burning is also normal and possibly always there when the pump is working but we just never noticed it before because there was no need to pay attention when the pump and water seemed to be working normally all the time. So there isn't necessarily anything wrong with the pump at all.

Could it be anything to do with the shower thermostatic valve. Maybe the scaldingly hot water from the tap is actually a sign of the cause of the problem. Maybe the shower is cutting out because the thermostatic shower valve is faulty/seized and it can't mix the scalding water to the set temp and is thus shutting off completely??

I'd like to have a better idea of what the problem might be before calling a plumber cause if I'm not there and a plumber tells other members of the household that it 'might' be the pump (cause he's not sure himself because the problem is intermittent and doesn't happen while he's there) and offers to replace, they'll agree straight away because they are worriers. We might end up with a cheaper nastier pump that still doesn't solve the problem but have handed out €500 for the privilege.