DHW luke warm

Hi everyone
I've had DHW supply issues ever since I moved into a new house in 2001. We live with very hard water! I'm a medical doctor (anaesthetist) with no plumbing knowledge, but not averse to bit of DIY! I wonder if anyone could help me with this problem.

The System:
Potterton Suprima 40
Gledhill Biolermate III

The Problem:
DHW supply weak and luke warm.
There has always been a difference between the behaviour of the sink DHW and the bath DHW.
The sink hot water has always been hot and strong until now, when the supply is adequate and less hot.
The bath hot water has never had a strong flow and we have always had to reduce the flow to maximise hot water temperature.
Now the bath hot water has a weaker maximum flow and is never hot, at best luke warm and very quickly cold.

Previous Repairs:
Boiler PCB replaced 2004
3 port valve actuator replaced 2008

Diagnostic tests:
I made an attempt at "resetting" the Boilermate Control PCB. I followed the "Comissoning the Boilermate Control System" instructions . Switch off mains, hold SW1 and SW2 and turn on mains. LCD display showed 888 and nothing else happened. No LED's flashing etc. Turned off and on again to get back to "normal" state. When DHW and CH are both off the LCD shows middle LED bar only on and "on".

Turned DHW on at single mechanical timer. No LED's, LED Bar 2 on, 3 port valve to hot water side (far left for me).
Turned CH on at room thermastat. LED 2,3,4 on, LED Bar 1 and 2 on, 3 port valve to CH side (far right). 2 mins later 3 port valve to mid point and LED's 1,2,3 on.
Turned CH off at room thermastat. LED 1,2 on, LED Bar 2 on, 3 port valve to hot water side.
Turned sink hot tap on LED Bar 2 and 3 on. Hot water pump on.
Eventually all LED's out as is supposed to happen when store temp reached.

Temp Sensor readings:
Store_T1: 76 68 75
PHE_T2: 40 69 75
DHW_T3:
DHW on, CH off, All taps closed 57
Sink tap on full 39
Bath tap on half 37
Bath tap on full 40

Workround:
If we turn the CH off (so 3 port valve is far left) and run the bath very slow DHW temp is just about OK.
If 3 port is at mid point DHW temp is low.

If any of this makes sense I would be most grateful for some pointers. I am guessing I've got a furred up Plate Heat Exchanger, but would be nice to know if anyone agrees.
Regards
Phil

Very comprehensive detail well done.
First thing I would check is;
Drain some water from the unit and ensure water is entering via the header tank.
This will prove if the unit is full and not sludged up too much.
If that is all ok.
I would check that the boiler is on max.
Then heat the store and ensure it is fully heated up.
Then try the hot water.
You could have sensor problems.
The domestic hot water pump could be at fault.
The mixer / blending valve also.
Or the plate heat exchanger.
Being 10 years old I would think the PHE would need de scaling. And a new blending valve to.
What is the cold water pressure like compared to the hot water pressure.
If the pressure of the hot is a lot less then it is a scaled PHE.
But as in a lot of case you could have more than one thing wrong.
Have you spoken to neighbours ref their units?
Oh and check under the bath hot tap for scale too.
Mike
MGC/H2O
Norfolk

Thanks Mike.
Boiler is on max.
Have tried hot water just after store reaches temp. The hot water is reasonably hot for about 30 secs.
Good idea to check bath tap not blocked!
There is enormous difference between hot and cold water pressure.
Will drain some water off and check filling...how?...just listen?
Not sure how to check pump? It's very quiet. I have been turning the speed from max to mid and back just to tell if it's on.

Hi Phil,

To check the pump take off the pump bleed vent with a screwdriver and with a tap open see if the internal screw is moving, if you have access to a multi meter also check the voltage at the pump.

If there is a big difference between the hot and cold water pressure then i am afraid to say that you will need to either descale or replace the plate heat exchanger, it will be full of lime scale. In my opinion its cheaper to replace if employing a plumber to do it, due to the labour cost.

hope this helps

Kind regards

Gary
MK Group

When draining off the cylinder, (drain valve at the bottom) if a ball valve is fitted at the top (in the F & E Tank) it should automatically refill or if not you should see the water level reduce in the F & E tank, If the water level drops then refill if not you have a blocked cold feed.

Gary
MK Group

Thanks Gary
Won't get to do further checks for a few days.
Will inform you both of progress.

Not jumping the gun here, just thinking ahead! Still got to check the cold feed and the pump. Sorry for all the questions, but here we go anyway!

Have just had a text walk through for changing the PHE from a "friend" who is a BG plumber. Not friendly enough to come and do it for me! He says I should drain the whole system (rads as well). I got the impression that that wasn't necessary from elsewhere on the forum. Can you just drain the storage cylinder to below the PHE? If so how do you know how far down you have drained the cylinder? Is it perhaps wiser to fully drain as you're doing the job anyway?

When you say the "mixer/blender" valve do you mean the 3 port electrically switched valve which blends between CH and DHW or the "mixing" valve which appears to divert mains cold water into the hot output from the PHE? Also, I'm thinking if I'm draining the system for the PHE I should change which ever mixer valve you refer to as if one is furred up then so will the other be. What do you think?

He also said to use "card" washers when fitting the new PHE, does he mean "fibre"?
I really am very grateful for the help your are giving me. Not least of all because it might save me a bomb!

I finally got round to checking pump and cylinder cold supply.
Pump definitely going round as tested by taking the screw cover off and feeling the shaft going around with a screwdriver.
Cold Supply
I tried to part-drain the cylinder but it would only drain at a dribble and eventually stopped after about 2 litres. It was as if nothing was entering to replace the drained water. I also turned off the cold supply to the header tank after testing the ball cock was working. When I had drained the 2-3 litres off and turned the header supply back on, the header tank did not fill at all as if the level had not gone down. Have I missed something out in the draining procedure?

Sounds like you have a blocked cold feed.

So, what's the mechanism by which that affects the hot water. Is it that the cylinder is not full so it has reduced thermal storage capacity?
And the solution? Can I unblock it? Do I have to add a new feed?

Take the F & E tank off the top and try to push water through the cylinder with the drain valve open.

A long job and not always succesful!

Good luck.

Gary
MK Group Limited

Today I took the FE tank off. I poked a 6 foot wire down the cold feed pipe and it was not blocked. So I checked the expansion pipe was clear too, cleaned the sludge out of the FE tank, flushed its pipes and put it back. Whilst the tank was off I tried to drain the cylinder and it still would not drain unless I poked a small screwdriver inside the drain plug. When I did this it drained slightly faster.

So I am thinking that the drain plug is either not opening properly or is blocked with sludge.

My next plan therefore is to drain the system from a lower point, maybe even the whole system, and take the cylinder drain plug out. Then I will be able to see how deep the sludge is in the cylinder, fit a new drain plug and flush the cylinder. I will replace the PHE at the same time.

Am I talking sense?
Regards
Phil

Sounds like a plan!

Gary

MK Group Ltd

Thanks Gary

Todays the day!
Drained system - tick!
Fitted PHE - tick!
Filled system - ah well...wondered why it wasn't filling....the FE tank water level as set by the ball cock does not reach the cold feed pipe! Furthermore it cannot be adjusted to fill that high! Surely that's odd.
Anyway, just holding ball valve open for a few hours!

[Edit]
Just been knocked by neighbour cos overflow poring! I was filling the world! So the overflow from the FE tank is the same height as the cold feed pipe! I'm confused! Never mind it's full up now. Still confused by this though.
Waiting for store to heat up to temp.

Up to temp. Heating appears to work. Hot water now very fast and freezing cold! Is it possible to put the PHE the wrong way up? DHW pump starting and very hot but hot water not circulating into PHE. Pipes either side of PHE on pump/store side are cold.
[Edit]
Correction, DHW pump is on all the time! Even when hot taps off.
Help!!!!

Undid a union above the valve above the PHE (Store side) and it was dry. So cylinder filled up to about 1 foot from the top. Took FE tank off again. Filled cylinder with hose down cold feed. Put back together and HOT water coming out my ears!! Thanks for all your help.

PS I think the expansion pipe might be blocked and that's why it didn't fill from the FE tank as no air getting out. Will it explode?

Get it sorted asap, if the expansion pipe is blocked then it could burst the tank.

Kind regards

Gary
MK Group Ltd

How far into the tank does the expansion pipe go? It's clear to about the depth of the tank.

Remove the F & E Tank, connect a drain hose and put a mains feed down the expansion pipe to clear the blockage.

Kind regards

Gary
MK Group

Thanks

I'm looking at a similar problem it seems: after draining the system, cold water is not entering main tank from F&E tank.

Just to test, I removed F&E tank and put thin semi-rigid plastic rod down cold feed, and it went down full height of tank, so I'm guessing its blocked right at the bottom? I poured water in cold feed and it doesn't go down (well, not at a noticeable speed). After seeing another post, I filled tank using draining tap (which was quite messy, the tap seems to leak a lot). The vent pipe must be clear because when the tank was full, it overflowed back into F&E.

After reading through this post it sounds like I should try forcing water down cold feed to try to unblock? Given that vent is free, can I keep drain tap closed? Any tips on getting a reasonably good seal around cold feed opening?

Thanks,

Alex

I have to say that although at times during the solving of my problem it appeared that both or either the cold feed or expansion pipe were blocked, I wonder if neither actually was! Like you I tried long semi-rigid rods which travelled to the depth of the cylinder. I wondered if I might have unblocked the pipes doing this and didn't realise? I also think I incorrectly identified the cold feed and expansion pipe, mixing them up. I say this because, in retrospect, the arrangement inside the F & E Tank means I MUST have got them the wrong way round.

The expansion pipe enters the F & E Tank through its base but travels a further 6 inches or so upwards to finish at the same level as the overflow of the F & E Tank. Clearly a cold feed would not function like that!!!

So I think when I thought I was manually refilling with a hose down the cold feet (F&E Tank off) I was actually refilling down the expansion pipe!!
This could all mean I might still have a blocked cold feed! I'd better investigate. But there again the air must have been able to displace out of the tank somehow as I was filling it.

What I would really like to know is the anatomy of the inside of my Gledhill Boilermate. Anyone know of any diagrams available?